Pumped heat electric storage system with recirculation

ABSTRACT

The present disclosure provides pumped thermal energy storage systems that can be used to store and extract electrical energy. A pumped thermal energy storage system of the present disclosure can store energy by operating as a heat pump or refrigerator, whereby net work input can be used to transfer heat from the cold side to the hot side. A working fluid of the system is capable of efficient heat exchange with heat storage fluids on a hot side of the system and on a cold side of the system. The system can extract energy by operating as a heat engine transferring heat from the hot side to the cold side, which can result in net work output.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. nationalization under 35 U.S.C. § 371 ofInternational Application No. PCT/US2020/060700, filed 16 Nov. 2020,which claims the benefit of priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 62/936,491, filed Nov. 16, 2019, andU.S. Provisional Patent Application No. 63/113,386, filed Nov. 13, 2020.The disclosures set forth in the referenced applications areincorporated herein by reference in their entirety.

BACKGROUND

In a heat engine or heat pump, a heat exchanger may be employed totransfer heat between a thermal storage material and a working fluid foruse with turbomachinery. The heat engine may be reversible, e.g., it mayalso be a heat pump, and the working fluid and heat exchanger may beused to transfer heat or cold to thermal storage media.

SUMMARY

A Pumped Heat Electric Storage (“PHES”) system may include at least aworking fluid circulated through a closed cycle fluid path including atleast two heat exchangers, at least one turbine, and at least onecompressor. In some systems, one or more recuperative heat exchangersmay also be included. At least two thermal reservoirs may hold thermalfluids which may be sent through the heat exchangers, providing thermalenergy to, and/or extracting thermal energy from, the working fluid. Oneor more motor/generators may be used to obtain work from the thermalenergy in the system, preferably by generating electricity frommechanical energy received from the turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates operating principles of a pumped heatelectric storage system.

FIG. 2 is a top-level schematic diagram of a PHES system, according toan example embodiment.

FIG. 3 is a schematic fluid path diagram of a working fluid loopsubsystem in a PHES system, according to an example embodiment.

FIGS. 3A-3D are schematic fluid path diagrams of a generation powertrainsystem and associated valves, according to example embodiments.

FIGS. 3E-3H are schematic fluid path diagrams of a charge powertrainsystem and associated valves, according to example embodiments.

FIGS. 3I-3J are schematic fluid path diagrams of an ambient coolersystem and associated valves, according to example embodiments.

FIGS. 3K-3L are schematic fluid path diagrams of an ambient coolersystem and associated valves, according to example embodiments.

FIG. 3M is a schematic fluid path diagram of an inventory controlsystem, according to an example embodiment.

FIG. 3N is a schematic fluid path diagram of circulatory flow pathsduring charge mode.

FIG. 3O is a schematic fluid path diagram of circulatory flow pathsduring generation mode.

FIG. 4 is a schematic fluid path diagram of a hot-side thermal storagesystem, according to an example embodiment.

FIG. 5 is a schematic fluid path diagram of a cold-side thermal storagesystem, according to an example embodiment.

FIG. 6A is a schematic fluid path diagram of a main heat exchangersystem, according to an example embodiment.

FIG. 6B is a schematic fluid path diagram of a main heat exchangersystem, according to an example embodiment.

FIG. 7 is a schematic diagram of a generation powertrain (“GPT”) system,according to an example embodiment.

FIG. 8 is a schematic diagram of a charge powertrain (“CPT”) system,according to an example embodiment.

FIG. 9 is a schematic electrical diagram of a power interface, accordingto an example embodiment.

FIG. 10 illustrates primary modes of operation of a PHES system,according to an example embodiment.

FIG. 11 is a state diagram illustrating operating states of a PHESsystem, according to an example embodiment.

FIG. 12 is a state diagram illustrating select operating andtransitional states of a PHES system, according to an exampleembodiment.

FIG. 13 is a state diagram illustrating select operating andtransitional states of a PHES system, according to an exampleembodiment.

FIG. 14 is a state diagram illustrating generation powertrain states ofa PHES system, according to an example embodiment.

FIG. 15 is a state diagram illustrating charge powertrain states of aPHES system, according to an example embodiment.

FIG. 16 is a state diagram illustrating generation powertrain valvestates of a PHES system, according to an example embodiment.

FIG. 17 is a state diagram illustrating charge powertrain valve statesof a PHES system, according to an example embodiment.

FIG. 18 is a state diagram illustrating ambient cooler states of a PHESsystem, according to an example embodiment.

FIG. 19 is a state diagram illustrating select operating andtransitional states of a PHES system, according to an exampleembodiment.

FIG. 20 is a state diagram illustrating select operating andtransitional states of a PHES system, according to an exampleembodiment.

FIG. 21 is a state diagram illustrating select operating andtransitional states of a PHES system, according to an exampleembodiment.

FIG. 22 is a state diagram illustrating select operating andtransitional states of a PHES system, according to an exampleembodiment.

FIG. 23 is a state diagram illustrating select operating andtransitional states of a PHES system, according to an exampleembodiment.

FIG. 24 illustrates select controllers that can be implemented in a PHESsystem, according to an example embodiment.

FIG. 25 is a state diagram illustrating hot-side loop states of a PHESsystem, according to an example embodiment.

FIG. 26 is a state diagram illustrating cold-side loop states of a PHESsystem, according to an example embodiment.

DETAILED DESCRIPTION

I. Overview

The Pumped Heat Electric Storage (“PHES”) systems, modes of operations,and states disclosed herein, as illustrated via multiple embodiments,are grid-scale energy storage systems that provide dispatchable powergeneration and power absorption. Advantageously, the PHES systems mayprovide increased grid stability and resilience. Additionally oralternatively, embodiments disclosed herein can achieve very fastdispatch response times, with spinning reserve capabilities comparableto natural gas peaker and cyclic units, but without the fossil fuelconsumption. The PHES systems disclosed herein, utilizing thermalstorage media also disclosed herein, may advantageously provide a safe,non-toxic and geography-independent energy (e.g., electricity) storagealternative.

The PHES systems function as thermodynamic cycle power generation and/orenergy storage systems. Embodiments of the PHES systems may work asBrayton cycle systems. Alternatively or additionally, embodiments of thePHES systems may work as reversible Brayton cycle systems. Preferably,the PHES systems may operate as closed working-fluid loop systems. ThePHES systems may use one or more generator and/or motor systems, whichconnect to one or more turbines and/or compressors which act on aworking fluid (e.g., air) circulating in the system.

The PHES systems may have a hot side and a cold side. Each side mayinclude one or more heat exchanger systems coupled to one or morethermal reservoirs. The PHES systems may employ liquid thermal storagemedium on both or either the hot side and/or the cold side. The liquidthermal storage media preferably include liquids that are stable at hightemperatures, such as molten nitrate salt or solar salt, and/or liquidsthat are stable at low temperatures, such as methanol/water coolantmixtures, glycols, and/or alkanes such as hexane. In one embodiment,cold-side and hot-side thermal reservoirs may include tanks of liquidthermal storage media, such as, but not limited to, methanol/watercoolant and molten salt, respectively.

During a charge cycle (i.e, charge mode), the PHES systems act as a heatpump, converting electrical energy from an electrical grid or othersource to thermal energy that is stored in thermal reservoirs. Theheat-pumping action may be done via motor-driven turbomachinery (e.g., acompressor system and a turbine system) in a closed-loop Brayton cycleusing a working fluid (e.g., air).

During a generation cycle (i.e., generation mode), the PHES systems actas a heat engine, converting stored thermal energy from the thermalreservoirs to electrical energy that can be dispatched back to the gridor another load. The working fluid loop during generation may be aclosed-loop Brayton cycle, may use the same working fluid as the chargecycle, may use the same or different heat exchangers as the chargecycle, and may use the same turbomachinery as the charge cycle or mayuse different turbomachinery than the charge cycle. The generationturbine system may drive one or more generators that are gridsynchronous.

Embodiments of the disclosed PHES systems enable fast cycling from fullcharge to full discharge.

Embodiments of the PHES systems also enable fast mode switching, suchthat the PHES system can switch modes from full load (i.e., charge) tofull generation in a very short duration. This is particularly usefulfor providing spinning reserve type capabilities to address energyshifting needs related to high penetration of solar (e.g., photovoltaic)energy generation on an electrical grid or grid segment. During rampperiods when solar generation is coming online or going offline, theability of the PHES systems to quickly change from full load to fullgeneration is critical for helping to address slope of the solar “duckcurve” that reflects a timing imbalance between peak demand andrenewable energy production.

Embodiments of the PHES systems also enable partial turndown. Variouspower generation applications (e.g. wind farms, natural gas peaker powerplants) benefit from the ability for generation and load assets such asthe PHES systems to ramp power up and down from full power based on adispatching signal.

FIG. 1 schematically illustrates operating principles of the PHESsystems. Electricity may be stored in the form of thermal energy of twothermal storage media at different temperatures (e.g., thermal energyreservoirs comprising thermal storage media such as heat storage fluids)by using one or more heat pump and heat engine systems. In a charging(heat pump) mode, work may be consumed by the PHES system fortransferring heat from a cold thermal medium to a hot thermal medium,thus lowering the temperature of the cold thermal medium and increasingthe temperature of the hot thermal medium. In a generation (heat engineor discharging) mode, work may be produced by the PHES systems bytransferring heat from the hot thermal medium to the cold thermalmedium, thus lowering the temperature (i.e., sensible energy) of the hotthermal medium and increasing the temperature of the cold thermalmedium. The PHES systems may be configured to ensure that the workproduced by the system during generation is a favorable fraction of theenergy consumed during charge. Excess heat from inefficiency may bedumped to ambient or an external heat sink. The PHES systems areconfigured to achieve high roundtrip efficiency, defined herein as thework produced by the system during generation divided by the workconsumed by the system during charge. Further, the design of the PHESsystems permits high roundtrip efficiency using components of a desired(e.g., acceptably low) cost.

The PHES systems may include a working fluid to and from which heat istransferred while undergoing a thermodynamic cycle. The PHES systemsoperating in a closed cycle allows, for example, a broad selection ofworking fluids, operation at elevated cold side pressures, operation atlower cold side temperatures, improved efficiency, and reduced risk ofcompressor and turbine damage. One or more aspects of the disclosuredescribed in relation to the PHES systems having working fluidsundergoing closed thermodynamic cycles may also be applied to the PHESsystems having working fluids undergoing open or semi-open thermodynamiccycles.

The working fluid may undergo a thermodynamic cycle operating at one,two, or more pressure levels. For example, the working fluid may operatein a closed cycle between a low-pressure limit on a cold side of thesystem and a high-pressure limit on a hot side of the system. In someimplementations, a low-pressure limit of about 10 atmospheres (atm) orgreater can be used. In some instances, the low pressure limit may be atleast about 1 atm, at least about 2 atm, at least about 5 atm, at leastabout 10 atm, at least about 15 atm, at least about 20 atm, at leastabout 30 atm, at least about 40 atm, at least about 60 atm, at leastabout 80 atm, at least about 100 atm, at least about 120 atm, at leastabout 160 atm, or at least about 200 atm, 500 atm, 1000 atm, or more. Insome instances, a sub-atmospheric low-pressure limit may be used. Forexample, the low-pressure limit may be less than about 0.1 atm, lessthan about 0.2 atm, less than about 0.5 atm, or less than about 1 atm.In some instances, the low-pressure limit may be about 1 atmosphere(atm). In the case of a working fluid operating in an open cycle, thelow-pressure limit may be about 1 atm or equal to ambient pressure.

Working fluids used in embodiments of the PHES systems may include air,argon, other noble gases, carbon dioxide, hydrogen, oxygen, or anycombination thereof, and/or other fluids in gaseous state throughout theworking fluid loop. In some implementations, a gas with a high specificheat ratio may be used to achieve higher cycle efficiency than a gaswith a low specific heat ratio. For example, argon (e.g., specific heatratio of about 1.66) may be used rather than air (e.g., specific heatratio of about 1.4). In some cases, the working fluid may be a blend ofone, two, three, or more fluids. In one example, helium (having a highthermal conductivity and a high specific heat) may be added to theworking fluid (e.g., argon) to improve heat transfer rates in heatexchangers.

The PHES systems may utilize thermal storage media, such as one or moreheat storage fluids. Alternatively or additionally, the thermal storagemedia may be solids or gasses, or a combination of liquids, solids,and/or gasses. The PHES systems may utilize a thermal storage medium ona hot side of the PHES system (“HTS medium”) and a thermal storagemedium on a cold side of the system (“CTS medium”). Preferably, thethermal storage media have high heat capacities per unit volume (e.g.,heat capacities above about 1400 Joule (kilogram Kelvin)−1) and highthermal conductivities (e.g., thermal conductivities above about 0.7Watt (meter Kelvin)−1). In some implementations, several differentthermal storage media on either the hot side or the cold side, or boththe hot side and the cold side, may be used.

The operating temperatures and pressures of the HTS medium may beentirely in the liquid range of the HTS medium, and the operatingtemperatures and pressures of the CTS medium may be entirely in theliquid range of the CTS medium. In some examples, liquids may enable amore rapid exchange of large amounts of heat than solids or gases. Thus,in some cases, liquid HTS and CTS media may advantageously be used.

In some implementations, the HTS medium may be a molten salt or amixture of molten salts. A salt or salt mixture that is liquid over theoperating temperature range of the HTS medium may be employed. Moltensalts can provide numerous advantages as thermal storage media, such aslow vapor pressure, lack of toxicity, chemical stability, low reactivitywith typical steels (e.g., melting point below the creep temperature ofsteels, low corrosiveness, low capacity to dissolve iron and nickel),and low cost. In one example, the HTS medium is a mixture of sodiumnitrate and potassium nitrate. In another example, the HTS medium is aeutectic mixture of sodium nitrate and potassium nitrate. In anotherexample, the HTS medium is a mixture of sodium nitrate and potassiumnitrate having a lowered melting point than the individual constituents,an increased boiling point than the individual constituents, or acombination thereof. Other examples of HTS media include potassiumnitrate, calcium nitrate, sodium nitrate, sodium nitrite, lithiumnitrate, mineral oil, or any combination thereof. Further examplesinclude any gaseous (including compressed gases), liquid or solid media(e.g., powdered solids) having suitable (e.g., high) thermal storagecapacities and/or are capable of achieving suitable (e.g., high) heattransfer rates with the working fluid. For example, a mix of 60% sodiumnitrate and 40% potassium nitrate (also referred to as a solar salt) canhave a heat capacity of approximately 1500 Joule (Kelvin mole)−1 and athermal conductivity of approximately 0.75 Watt (meter Kelvin)−1 withina temperature range of interest. Advantageously, the HTS medium may beoperated in a temperature range that is compatible with structuralsteels used in unit components of the PHES system.

In some cases, liquid water at temperatures of about 0° C. to 100° C.(about 273 K-373 K) and a pressure of about 1 atm may be used as the CTSmedium. Due to a possible explosion hazard associated with the presenceof steam at or near the boiling point of water, the operatingtemperature can be kept below 100° C. while maintaining an operatingpressure of 1 atm (i.e., no pressurization). In some cases, thetemperature operating range of the CTS medium may be extended (e.g., to−30° C. to 100° C. at 1 atm) by using a mixture of water and one or moreantifreeze compounds (e.g., ethylene glycol, propylene glycol, orglycerol), or a water/alcohol mixture such as water and methanol.

Improved efficiency may be achieved by increasing the temperaturedifference at which the PHES system operates, for example, by using aCTS medium capable of operating at lower temperatures. In some examples,the CTS medium may comprise hydrocarbons, such as, for example, alkanes(e.g., hexane or heptane), alkenes, alkynes, aldehydes, ketones,carboxylic acids (e.g., HCOOH), ethers, cycloalkanes, aromatichydrocarbons, alcohols (e.g., butanol), other type(s) of hydrocarbonmolecules, or any combinations thereof. In some examples, cryogenicliquids having boiling points below about −150° C. or about −180° C. maybe used as CTS medium (e.g., propane, butane, pentane, nitrogen, helium,neon, argon, krypton, air, hydrogen, methane, or liquefied natural gas,or combinations thereof). In some implementations, choice of CTS mediummay be limited by the choice of working fluid. For example, when agaseous working fluid is used, a liquid CTS medium having a liquidtemperature range at least partially or substantially above the boilingpoint of the working fluid may be required.

In some cases, the operating temperature range of CTS and/or HTS mediacan be changed by pressurizing (i.e., raising the pressure) orevacuating (i.e., lowering the pressure) the thermal media fluid pathsand storage tanks, and thus changing the temperature at which thestorage media undergo phase transitions.

The HTS medium and/or CTS medium may be in a liquid state over all, orover at least a portion, of the operating temperature range of therespective side of a PHES system. The HTS medium and/or CTS medium maybe heated, cooled or maintained to achieve a suitable operatingtemperature prior to, during or after various modes of operation of aPHES system.

The thermal reservoirs of the PHES systems may cycle between charged anddischarged modes, in conjunction with, or separate from, the charge andgeneration cycles of the overall PHES system embodiment. In someexamples, the thermal reservoirs of the PHES systems may be fullycharged, partially charged or partially discharged, or fully discharged.In some cases, cold-side thermal reservoir(s) may be charged (also“recharged” herein) independently from hot-side thermal reservoir(s).Further, in some implementations, charging (or some portion thereof) ofthermal reservoirs and discharging (or some portion thereof) of thermalreservoirs can occur simultaneously. For example, a first portion of ahot-side thermal reservoir may be recharged while a second portion ofthe hot-side thermal reservoir together with a cold-side thermalreservoir are being discharged.

Embodiments of the PHES systems may be capable of storing energy for agiven amount of time. In some cases, a given amount of energy may bestored for at least about 1 second, at least about 30 seconds, at leastabout 1 minute, at least about 5 minutes, at least about 30 minutes, atleast about 1 hour, at least about 2 hours, at least about 3 hours, atleast about 4 hours, at least about 5 hours, at least about 6 hours, atleast about 7 hours, at least about 8 hours, at least about 9 hours, atleast about 10 hours, at least about 12 hours at least about 14 hours,at least about 16 hours, at least about 18 hours, at least about 20hours, at least about 22 hours, at least about 24 hours (1 day), atleast about 2 days, at least about 4 days, at least about 6 days, atleast about 8 days, at least about 10 days, 20 days, 30 days, 60 days,100 days, 1 year or more.

Embodiments of the PHES systems may be capable of storing/receivinginput of, and/or extracting/providing output of, a substantially largeamount of energy for use with power generation systems (e.g.,intermittent power generation systems such as wind power or solarpower), power distribution systems (e.g. electrical grid), and/or otherloads or uses in grid-scale or stand-alone settings. During a chargemode of the PHES systems, electric power received from an external powersource (e.g., a wind power system, a solar photovoltaic power system, anelectrical grid etc.) can be used to operate the PHES systems in theheat pump mode (i.e., transferring heat from a low temperature reservoirto a high temperature reservoir, thus storing energy). During ageneration mode of the PHES systems, the system can supply electricpower to an external power system or load (e.g., one or more electricalgrids connected to one or more loads, a load, such as a factory or apower-intensive process, etc.) by operating in the heat engine mode(i.e., transferring heat from a high temperature reservoir to a lowtemperature reservoir, thus extracting energy). As described elsewhereherein, during charge and/or generation, the system may receive orreject thermal power, including, but not limited to electromagneticpower (e.g., solar radiation) and thermal power (e.g., sensible energyfrom a medium heated by solar radiation, heat of combustion etc.).

In some implementations, the PHES systems are grid-synchronous.Synchronization can be achieved by matching speed and frequency ofmotors and/or generators and/or turbomachinery of a system with thefrequency of one or more grid networks with which the PHES systemsexchange power. For example, a compressor and a turbine can rotate at agiven, fixed speed (e.g., 3600 revolutions per minute (rpm)) that is amultiple of North American grid frequency (e.g., 60 hertz (Hz)). In somecases, such a configuration may eliminate the need for additional powerelectronics. In some implementations, the turbomachinery and/or themotors and/or generators are not grid synchronous. In such cases,frequency matching can be accomplished through the use of powerelectronics. In some implementations, the turbomachinery and/or themotors and/or generators are not directly grid synchronous but can bematched through the use of gears and/or a mechanical gearbox. Asdescribed in greater detail elsewhere herein, the PHES systems may alsobe power and/or load rampable. Such capabilities may enable thesegrid-scale energy storage systems to operate as peaking power plantsand/or as a load following power plants. In some cases, the PHES systemsof the disclosure may be capable of operating as base load power plants.

Embodiments of the PHES systems can have a given power capacity. In somecases, power capacity during charge may differ from power capacityduring discharge. For example, embodiments of the PHES system can have acharge and/or discharge power capacity of less than about 1 megawatt(MW), at least about 1 megawatt, at least about 2 MW, at least about 3MW, at least about 4 MW, at least about 5 MW, at least about 6 MW, atleast about 7 MW, at least about 8 MW, at least about 9 MW, at leastabout 10 MW, at least about 20 MW, at least about 30 MW, at least about40 MW, at least about 50 MW, at least about 75 MW, at least about 100MW, at least about 200 MW, at least about 500 MW, at least about 1gigawatt (GW), at least about 2 GW, at least about 5 GW, at least about10 GW, at least about 20 GW, at least about 30 GW, at least about 40 GW,at least about 50 GW, at least about 75 GW, at least about 100 GW, ormore.

Embodiments of the PHES systems can have a given energy storagecapacity. In one example, a PHES system embodiment may be configured asa 100 MW unit operating for 10-hour cycles. In another example, a PHESsystem embodiment may be configured as a 1 GW plant operating for12-hour cycles. In some instances, the energy storage capacity can beless than about 1 megawatt hour (MWh), at least about 1 megawatt hour,at least about 10 MWh, at least about 100 MWh, at least about 1 gigawatthour (GWh), at least about 5 GWh, at least about 10 GWh, at least about20 GWh, at least 50 GWh, at least about 100 GWh, at least about 200 GWh,at least about 500 GWh, at least about 700 GWh, at least about 1000 GWh,or more.

In some cases, a given power capacity may be achieved with a given size,configuration and/or operating conditions of the heat engine/heat pumpcycle. For example, size of turbomachinery and/or heat exchangers,number of turbomachinery and/or heat exchangers, or other systemcomponents, may correspond to a given power capacity.

In some implementations, a given energy storage capacity may be achievedwith a given size and/or number of hot-side thermal reservoir(s) and/orcold-side thermal reservoir(s). For example, the heat engine/heat pumpcycle can operate at a given power capacity for a given amount of timeset by the heat storage capacity of the thermal reservoir(s). The numberand/or heat storage capacity of the hot-side thermal reservoir(s) may bedifferent from the number and/or heat storage capacity of the cold-sidethermal reservoir(s). The number of thermal reservoir(s) may depend onthe size of individual thermal reservoir(s).

Embodiments of the PHES systems may include any suitable number ofcold-side and/or hot-side thermal storage units (e.g., CTS medium and/orHTS medium storage tanks, respectively), such as, but not limited to, atleast about 1 (divided into two sections), at least about 2, at leastabout 4, at least about 10, at least about 50, at least about 100, andthe like. In some examples, embodiments of the PHES system include 2, 3,4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, or morethermal storage units (e.g., CTS medium and/or HTS medium storagetanks).

While various embodiments of the invention are shown and describedherein, it will be obvious to those skilled in the art that suchembodiments are provided by way of example only. Numerous variations,changes, and substitutions may occur to those skilled in the art withoutdeparting from the invention. It should be understood that variousalternatives to the embodiments of the invention described herein may beemployed. It shall be understood that different aspects of the inventioncan be appreciated individually, collectively, or in combination witheach other.

It is to be understood that the terminology used herein is used for thepurpose of describing specific embodiments, and is not intended to limitthe scope of the present invention. It should be noted that as usedherein, the singular forms of “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. In addition,unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

While preferable embodiments of the present invention are shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

The term “reversible,” as used herein, generally refers to a process oroperation that can be reversed. In some examples, in a reversibleprocess, the direction of flow of energy is reversible. As analternative, or in addition to, the general direction of operation of areversible process (e.g., the direction of fluid flow) can be reversed,such as, e.g., from clockwise to counterclockwise, and vice versa.

The term “sequence,” as used herein, generally refers to elements (e.g.,unit operations) in order. Such order can refer to process order, suchas, for example, the order in which a fluid flows from one element toanother. In an example, a compressor, heat exchange unit, and turbine insequence includes the compressor upstream of the heat exchange unit, andthe heat exchange unit upstream of the turbine. In such a case, a fluidcan flow from the compressor to the heat exchange unit and from the heatexchange unit to the turbine. A fluid flowing through unit operations insequence can flow through the unit operations sequentially. A sequenceof elements can include one or more intervening elements. For example, asystem comprising a compressor, heat storage unit and turbine insequence can include an auxiliary tank between the compressor and theheat storage unit. A sequence of elements can be cyclical.

II. Illustrative PHES System

FIG. 2 is a top-level schematic diagram of a PHES system 1000, accordingto an example embodiment, in which PHES system embodiments herein may beimplemented. As a top-level schematic, the example embodiment PHESsystem 1000 in FIG. 2 illustrates major subsystems and selectcomponents, but not all components. Additional components are furtherillustrated with respect to additional figures detailing varioussubsystems. Additionally or alternatively, in other embodiments,additional components and/or subsystems may be included, and/orcomponents and/or subsystems may not be included. FIG. 2 furtherillustrates select components and subsystems that work together in thePHES system 1000. FIG. 2 schematically shows how the select componentsand subsystems connect, how they are grouped into major subsystems, andselect interconnects between them.

In FIG. 2 and FIGS. 3, 3A-3O, 4-9 , connections between subsystems areillustrated as interconnects, such as fluid interconnects 3, 4 andelectrical interconnects 15, 21. Illustrated connections between fluidinterconnects, electrical interconnects, and/or components reflect fluidpaths or power/signal paths, as appropriate. For example, fluid path 901connects fluid interconnect 2 and fluid interconnect 3, thereby allowingfluid flow between CHX system 600 and AHX system 700, described infurther detail below. As another example, power/signal path 902 connectselectrical interconnect 15 and electrical interconnect 15A, which cancarry power/signals between power interface 2002 and motor system 110.Junctions between illustrated paths are shown as a solid dot. Forexample, fluid path 903 exiting the main heat exchanger system 300A atfluid interconnect 7 joins the fluid path 904 between fluid interconnect17 and fluid interconnect 23 at junction 905. Fluid paths may includecomponents, connections, valves, and piping between components, and eachfluid path may, in practice, include a single flow path (e.g., a singlepipe) or multiple (e.g. parallel) flow paths (e.g., multiple pipes)between components. Valves may interrupt or make fluid connectionsbetween various fluid paths, as elsewhere illustrated, such as in FIG. 3. Valves may be actively controllable through actuators or other knowndevices in response to control signals, or may change state (e.g., opento close) in response to a physical condition at the valve, such as anoverpressure condition at a pressure relief device. Further, valves mayinclude variable position valves (e.g., capable of partial flow such asin proportional or servo valves) or switching valves (e.g., either openor closed). If an illustrated valve is on a fluid path that in practiceincludes multiple flow paths (e.g., multiple pipes), then each flow pathmay connect to the single valve or there may be multiple valvesconnecting the multiple flow paths. For power/signal paths, switches,breakers, or other devices may interrupt or make power/signalconnections between various power/signal paths, such as in FIG. 9 .

Major subsystems of PHES system 1000 include a charge powertrain system(“CPT system”) 100, a generation powertrain system (“GPT system”) 200, aworking fluid loop 300, a main heat exchanger system 300A, a hot-sidethermal storage system (“HTS system”) 501, a cold-side thermal storagesystem (“CTS system”) 601, and site integration systems 2000.

In FIG. 2 , illustrated components in CPT system 100 include chargemotor system 110, charge gearbox system 120, charge compressor system130, and charge turbine system 140. Depending on operational mode,state, and embodiment configuration, CPT system 100 may connect to othercomponents and subsystems of PHES system 1000 through variousinterconnects, including electrical interconnect 15 and fluidinterconnects 17, 18, 19, and 20. Additionally, CPT system 100 mayinclude more or fewer interconnects than shown in FIG. 2 . The CPTsystem 100 takes electrical power in at electrical interconnect 15 andconverts the electrical energy to working fluid flows through one ormore of its fluid interconnects.

In FIG. 2 , illustrated components in GPT system 200 include generationmotor system 210, generation gearbox system 220, generation compressorsystem 230, and generation turbine system 240. Depending on operationalmode, state, and embodiment configuration, GPT system 200 may connect toother components and subsystems of PHES system 1000 through variousinterconnects, including electrical interconnect 21 and fluidinterconnects 22, 23, 25, and 26. Additionally, GPT system 200 mayinclude more or fewer interconnects than shown in FIG. 2 . GPT system200 outputs electrical power at electrical interconnect 21 by takingenergy from the working fluid flows through one or more of fluidinterconnects. In some operating conditions or states, GPT system 200may also receive power through one or more of electrical interconnects,such as electrical interconnect 21.

In FIG. 2 , working fluid loop 300 includes a main heat exchanger system300A, which includes recuperator heat exchanger (“RHX”) system 400,hot-side heat exchanger (“HHX”) system 500, cold-side heat exchanger(“CHX”) system 600, and ambient cooler (heat exchanger) (“AHX”) system700. Depending on operational mode, state, and embodiment configuration,components in the main heat exchanger system 300A may connect to othercomponents and subsystems of the PHES system 1000, and/or othercomponents within the main heat exchanger system 300A or the workingfluid loop 300, through various interconnects, including fluidinterconnects 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 28, and 29.

In FIG. 2 , working fluid loop 300 further includes the chargecompressor system 130, and charge turbine system 140 of the CPT system100, and the generation compressor system 230, and generation turbinesystem 240 of the GPT system 200. Depending on operational mode, state,and embodiment configuration, components in the working fluid loop 300may connect to other components and subsystems of the PHES system 1000,and/or other components within the working fluid loop 300, throughvarious interconnects, including fluid interconnects 17, 18, 19, 20, 22,23, 25, and 26.

In the PHES system 1000, working fluid loop 300 may act as a closedfluid path through which the working fluid circulates and in whichdesired system pressures of the working fluid can be maintained. Theworking fluid loop 300 provides an interface for the working fluidbetween the turbomachinery (e.g., charge compressor system 130 andcharge turbine system 140, and/or generation compressor system 230 andgeneration turbine system 240) and the heat exchangers in the main heatexchanger system 300A. In a preferred embodiment, the working fluid isair. Example embodiments, and portions thereof, of working fluid loop300, are illustrated in FIGS. 3 and 3A-O.

The working fluid loop 300 includes a fluid path that, in someoperational modes and/or states of PHES system 1000, carrieshigh-temperature and high-pressure working fluid between chargecompressor system 130 and HHX system 500. In other operational modesand/or states a fluid path carries high-temperature and high-pressureworking fluid between HHX system 500 and generation turbine system 240.Other configurations are possible as well. These configurations arefurther detailed with respect to the mode of operation and statedescriptions herein and FIGS. 3 and 3A-O.

The working fluid loop 300 includes a fluid path that, in someoperational modes and/or states of PHES system 1000, carriesmedium-temperature and high-pressure working fluid between RHX system400 and charge turbine system 140. In other operational modes and/orstates, a fluid path carries medium-temperature and high-pressureworking fluid between generation compressor system 230 and RHX system400. Other configurations are possible as well. These configurations arefurther detailed with respect to the mode of operation and statedescriptions herein and FIGS. 3 and 3A-O.

The working fluid loop 300 includes a fluid path that, in someoperational modes and/or states of PHES system 1000, carrieslow-temperature and low-pressure working fluid between charge turbinesystem 140 and CHX system 600. In other operational modes and/or statesa fluid path carries low-temperature and low-pressure working fluidbetween CHX system 600 and generation compressor system 230. Otherconfigurations are possible as well. These configurations are furtherdetailed with respect to the mode of operation and state descriptionsherein and FIGS. 3 and 3A-O.

The working fluid loop 300 includes a fluid path that, in someoperational modes and/or states of PHES system 1000, carriesmedium-temperature and low-pressure working fluid between RHX system 400and charge compressor system 130. In other operational modes and/orstates, a fluid path carries medium-temperature and low-pressure workingfluid between generation turbine system 240 and RHX system 400. Otherconfigurations are possible as well. These configurations are furtherdetailed with respect to the mode of operation and state descriptionsherein and FIGS. 3 and 3A-O.

The main heat exchanger system 300A facilitates heat transfer betweenthe working fluid circulating through the working fluid loop 300, a CTSmedium circulating from/to the CTS system 601, an HTX medium circulatingfrom/to the HTS system 501, and the ambient environment or other heatsink via AHX system 700. The CTS medium circulates between a warm CTSsystem 691 and a cold CTS system 692 via the CHX system 600, and thatcirculation may be referred to as the “CTS loop” or “cold-side loop,” asfurther described, e.g., with respect to a CTS system 601 embodimentillustrated in FIG. 5 . In a preferred embodiment, the CTS medium is acoolant fluid, such as a methanol and water mixture. The HTS mediumcirculates between a warm HTS system 591 and a hot HTS system 592 viathe HHX system 500, and that circulation may be referred to as the “HTSloop” or “hot-side loop,” as further described, e.g., with respect to anHTS system 601 embodiment illustrated in FIG. 4 . In a preferredembodiment, the HTX medium is a molten salt.

In FIG. 2 , illustrated components in CTS system 601 include arepresentation of a cold-side thermal reservoir, including warm CTSsystem 691 and cold CTS system 692. Depending on operational mode,state, and embodiment configuration, CTS system 601 may connect to othercomponents and subsystems of PHES system 1000 through variousinterconnects, including fluid interconnects 1 and 31. An exampleembodiment of CTS system 601, including pumps and supporting fluidpaths, valves, and other components is illustrated in FIG. 5 .

In FIG. 2 , illustrated components in HTS system 501 include arepresentation of a hot-side thermal reservoir, including warm HTSsystem 591 and hot HTS system 592. Depending on operational mode, state,and embodiment configuration, HTS system 501 may connect to othercomponents and subsystems of PHES system 1000 through variousinterconnects, including fluid interconnects 6 and 8. An exampleembodiment of HTS system 501, including pumps and supporting fluidpaths, valves, and other components is illustrated in FIG. 4 .

Components in PHES system 1000, including but not limited to valves,fans, sensors, pumps, heaters, heat traces, breakers, VFDs, workingfluid compressors, etc., may each be connected to a power source and maybe independently controllable, either or both proportionally and/orswitchably, via one or more controllers and/or control systems.Additionally, each such component may include, or be communicativelyconnected via, a signal connection with another such component, through,for example, a wired, optical, or wireless connections. For example, asensor may transmit data regarding temperature of the working fluid at alocation in the working fluid loop; and, a control system may receivethat data and responsively send a signal to a valve to close a fluidpath. Data transmission and component control via signaling is known inthe art and not illustrated herein, except wherein a particulararrangement is new and/or particularly relevant to the disclosed PHESsystems, as with, for example, FIG. 9 .

A. Charge Powertrain Subsystem

FIG. 8 is a schematic diagram of the charge powertrain system 100,according to an example embodiment. FIG. 8 provides additional detailconcerning CPT system 100 beyond that shown in the top-level schematicof FIG. 2 . The CPT system 100 may be implemented in PHES systemsdisclosed herein, including the PHES system 1000 embodiment illustratedin FIG. 2 . Other embodiments of a charge powertrain system operable inPHES systems disclosed herein are possible as well.

In FIG. 8 , CPT system 100 includes a motor 110-1 as part of the chargemotor system 110 of FIG. 2 , a gearbox 120-1 as part of the chargegearbox system 120 of FIG. 2 , a compressor 130-1 as part of chargecompressor system 130, and a turbine 140-1 as part of charge turbinesystem 140. These components are connected via a drivetrain 150, suchthat the motor 110-1 is capable of driving the gearbox 120-1, thecompressor 130-1, and the turbine 140-1. Drivetrain 150 may include afixed connection between compressor 130-1 and turbine 140-1, and/or mayinclude one or more shafts, flexible couplings, clutches, and/orgearboxes between compressor 130-1 and turbine 140-1. CPT system 100further includes a turning motor 121-1 that is additionally capable ofdriving the compressor 130-1 and/or the turbine 140-1. Within CPT system100, gearbox 120-1 provides a speed conversion between the motor 110-1and turning motor 121-1 and the turbomachinery. In other embodiments ofa charge powertrain system, the gearbox 120-1 may act only on one of themotors 110-1 and 121-1. Alternatively or additionally, gearbox 120-1 mayact only on motor 110-1 and another gearbox (or no gearbox) may act onturning motor 121-1. In another embodiment, gearbox 120-1 may beomitted, therefore resulting in no speed conversion.

Turning motor 121-1 may be used for spinning CPT system 100turbomachinery at low speeds (e.g., “slow roll”), for example, to coolthe compressor 130-1 following a shutdown, and before bringing therotating equipment to rest. The turning motor 121-1 may be mounted tothe gearbox 120-1 or the drivetrain 150 or the motor 110-1, orelsewhere, and preferably rotates the turbomachinery at a very low RPMcompared to the motor 110-1. The turning motor 121-1 is fitted with anoverrunning clutch 121-2 that disengages when the drivetrain 150 side ofthe clutch is operating at higher speeds than the turning motor 121-1.This results in the turning motor 121-2 engaging with the drivetrain 150when the slowing drivetrain 150 reaches the speed of the turning motor121-1. The turning motor 121-1 will then maintain the slow roll speed.

CPT system 100 can receive power into the subsystem (via, e.g.,electrical interconnect 15) and supply power to the motor system 110(e.g., motor 110-1) and/or the turning motor 121-1. Depending onoperational mode, state, and embodiment configuration, and as furtherillustrated in FIG. 2 , CPT system 100 may receive power via a powerinterface 2002 and from the generation system 210 and/or an externalsource such as an electrical grid or local external generation source(e.g., power plant, renewable energy source, etc.) via interconnect 27.

Depending on operational mode and state, compressor 130-1 may raise thepressure of working fluid flowing through the compressor 130-1 by usingrotational energy transmitted through the drivetrain 150. For example,during a charging mode (e.g., charge 1002 in FIG. 10 ), compressor 130-1will compress working fluid flowing through it. As another example,during a slow rolling mode (e.g., CPT slow rolling 1062 in FIG. 15 ),the compressor 130-1, though spinning (e.g., via torque from the turningmotor 121-1), may not cause an operationally significant increase inpressure of the working fluid.

Compressor 130-1 has at least one fluid inlet which connects to fluidinterconnect 20 and allows working fluid to enter the low-pressure sideof the compressor 130-1. Compressor 130-1 also has at least one fluidoutlet which connects to fluid interconnect 17 and allows working fluidto exit the high-pressure side of the compressor 130-1. The schematicillustration represented in FIG. 8 is not meant to limit the CPT system100 to a particular arrangement. For example, the turning motor 121-1may be oriented differently or located at a different location where itis still capable of turning the drivetrain 150. As another example,inlets and outlets to the turbomachinery may be located at sides otherthan the top, side, and ends depicted.

A variable frequency drive (“VFD”) (e.g., VFD 214 in FIG. 9 ) may beshared between the CPT system 100 and the GPT system 200. In oneembodiment, the VFD may be utilized for startup and slow-rolling of thesystem only and is configured to exert only positive loads on thedrivetrain 150. For example, VFD 214 may provide variable frequencypower to motor 110-1 during CPT system 100 spinup.

Depending on operational mode and state, turbine 140-1 may reduce thepressure (e.g., through expansion) of working fluid flowing through theturbine 140-1, and energy derived from that pressure reduction may betransformed into rotational energy in the drivetrain 150. Turbine 140-1has a fluid inlet which connects to fluid interconnect 18 and allowsworking fluid to enter the high-pressure side of the turbine 140-1.Turbine 140-1 also has a fluid outlet which connect to fluidinterconnect 19 and allows working fluid to exit the low-pressure sideof the turbine 140-1.

B. Generation Powertrain Subsystem

FIG. 7 is a schematic diagram of the generation powertrain system 200,according to an example embodiment. FIG. 7 provides additional detailconcerning GPT system 200 than is shown in the top-level schematic ofFIG. 2 . The GPT system 200 may be implemented in PHES systems disclosedherein, including the PHES system 1000 embodiment illustrated in FIG. 2. Other embodiments of a generation powertrain system operable in PHESsystems disclosed herein are possible as well.

In FIG. 7 , GPT system 200 includes a generator 210-1 as part of thegeneration system 210 of FIG. 2 , a gearbox 220-1 as part of thegeneration gearbox system 220 of FIG. 2 , a compressor 230-1 as part ofgeneration compressor system 230, and a turbine 240-1 as part ofgeneration turbine system 240. These components are connected via adrivetrain 250, such that the generator 210-1 is capable of being drivenby the gearbox 220-1 and the turbine 240-1, and vice-versa. Depending onoperational mode and system states, the generation system 210, andgenerator 210-1, may generate net positive electrical power that is thesent outside and/or elsewhere within the PHES system 1000. Additionally,depending on the operating condition and state, the generator 210-1 mayact as a motor. For example, during spinup of the GPT system 200, thegenerator 210-1 may receive electrical power and drive the gearbox 220-1and the turbomachinery. Drivetrain 250 may include a fixed connectionbetween compressor 230-1 and turbine 240-1, and/or may include one ormore shafts, flexible couplings, clutches, and/or gearboxes betweencompressor 230-1 and turbine 240-1.

GPT system 200 further includes a turning motor 221-1 that is capable ofdriving the compressor 230-1 and the turbine 240-1. Within GPT system200, gearbox 220-1 provides a speed conversion between the generator210-1 and turning motor 221-1 and the turbomachinery. In otherembodiments of a generation powertrain system, the gearbox 220-1 may actonly on one of the generator 210-1 and turning motor 221-1.Alternatively or additionally, gearbox 220-1 may act only on generator210-1 and another gearbox (or no gearbox) may act on turning motor221-1. In another embodiment, gearbox 220-1 may be omitted, thereforeresulting in no speed conversion

Turning motor 221-1 may be used for spinning GPT system 200turbomachinery under slow roll, for example, to cool the turbine 240-1following a shutdown, and before bringing the rotating equipment torest. The turning motor 221-1 may be mounted to the gearbox 220-1 or thedrivetrain 250 or the generator 210-1, or elsewhere, and preferablyrotates the turbomachinery at a very low RPM compared to normaloperational speed of the turbomachinery. The turning motor 221-1 isfitted with an overrunning clutch 221-2 that disengages when thedrivetrain 250 side of the clutch is operating at higher speeds. Thisresults in the turning motor 221-2 engaging with the drivetrain 250 whenthe slowing drivetrain 250 reaches the speed of the turning motor 221-1.The turning motor 221-1 will then maintain the slow roll speed.

GPT system 200 may send electrical power out of, and receive power into,the subsystem via electrical interconnect 21 and via power interface2002. Depending on operational mode, state, and embodimentconfiguration, the power interface 2002 may receive electrical powerfrom the generator 210-1 via electrical interconnect 21A and sendelectrical power to an external source, such as an electrical grid orother load via electrical interconnect 27. The power interface 2002 mayalso send electrical power from an electrical grid or other source toGPT system 200. The power interface 2002 may alternatively oradditionally route power received from the GPT system 200 to the CPTsystem 100.

Depending on operational mode and state, compressor 230-1 may raise thepressure of working fluid flowing through the compressor 230-1 by usingrotational energy transmitted through the drivetrain 250 from, e.g., theturbine 240-1. For example, during a generation mode (e.g., generation1004 in FIG. 10 ), compressor 230-1 will compress working fluid flowingthrough it. As another example, during a slow rolling mode (e.g., GPTslow rolling 1054 in FIG. 14 ), the compressor 230-1, though spinning(e.g., via torque from the turning motor 221-1), may not cause anoperationally significant increase in pressure of the working fluid.Compressor 230-1 has a fluid inlet which connects to fluid interconnect26 and allows working fluid to enter the low-pressure side of thecompressor 230-1. Compressor 230-1 also has a fluid outlet whichconnects to fluid interconnect 22 and allows working fluid to exit thehigh-pressure side of the compressor 230-1. The schematic illustrationrepresented in FIG. 7 is not meant to limit the GPT system 200 to aparticular arrangement. For example, the turning motor 221-1 may beoriented differently or located at a different location where it isstill capable of turning the drivetrain 250. As another example, inletsand outlets to the turbomachinery may be located at sides other than thetop, side, and ends depicted.

As previously disclosed, a VFD (e.g., VFD 214 in FIG. 9 ) may be sharedbetween the CPT system 100 and the GPT system 200. In one embodiment,the VFD may be utilized for startup and slow-rolling of the system onlyand is configured to exert only positive loads on the drivetrain 250.For example, VFD 214 may provide variable frequency power to generator210-1 during GPT system 200 startup.

Depending on operational mode and state, turbine 240-1 may reduce thepressure (e.g., through expansion) of working fluid flowing through theturbine 240-1, and energy derived from that pressure reduction may betransformed into rotational energy in the drivetrain 250. In some modesand states, that rotational energy may be used to rotate the compressor230-1 and/or generate electrical power at the generator 210-1. Turbine240-1 has one or more fluid inlets which connect to fluid interconnect23 and allow working fluid to enter the high-pressure side of theturbine 240-1. Turbine 240-1 also has a fluid outlet which connects tofluid interconnect 25 and allows working fluid to exit the low-pressureside of the turbine 240-1.

C. Site Integration Subsystem

FIG. 9 is a schematic electrical diagram of a power interface, accordingto an example embodiment, that can be implemented in power interface2002 in site integration subsystem 2000. Power interface 2000 includes aVFD 214, a VFD-to-generator breaker 211, a generator-to-grid breaker212, a VFD-to-charge-motor breaker 111, and a charge-motor-to-gridbreaker 112, with each component in power interface 2002 electricallyconnected as illustrated. Breakers can be set to closed or open mode andmay be remotely controlled. Other embodiments of a power interface mayinclude additional or fewer breakers, additional or fewer VFDs,different electrical connections, and/or additional components.

For spinning up the GPT system 200, VFD-to-generator breaker 211 can beclosed to connect VFD 214 to generation system 210 (e.g., generator210-1 and/or turning motor 221-1), thus routing power from an externalsource via electrical interconnect 27, through VFD 214, through breaker211, and to generation system 210. For generation mode,generator-to-grid breaker 212 can be closed to connect generation system210 (e.g., generator 210-1) to an external electrical grid or otherexternal load through electrical interconnects 21A and 27. For spinningup the CPT system 100, VFD-to-charge-motor breaker 111 can be closed toconnect VFD 214 to the motor system 110 (e.g., motor 110-1 and/orturning motor 121-1) in the CPT system 100 through electricalinterconnects 15A and 27. For charge mode, charge-motor-to-grid breaker112 can be closed to connect motor system 110 (e.g., motor 110-1) in theCPT system 100 to an external electrical grid or other electrical powersource through electrical interconnects 15A and 27.

D. Main Heat Exchanger Subsystem

FIGS. 6A and 6B are schematic fluid path diagrams of example embodimentsof main heat exchanger systems, that can be implemented as main heatexchanger system in a PHES system (e.g., PHES system 1000). FIGS. 6A and6B provide additional details, in separate embodiments, concerning mainheat exchanger system 300A than is shown in the top-level schematic ofFIG. 2 .

The main heat exchanger system 390 embodiment in FIG. 6A and/or the mainheat exchanger system 391 embodiment in FIG. 6B can be implemented asthe main heat exchanger system 300A in PHES system 1000, or otherdisclosed PHES systems. Other main heat exchanger system embodiments arealso possible. References herein to main heat exchanger system 300A canbe understood with reference to embodiments 390 and/or 391.

In general terms, main heat exchanger system 300A consists of fourdifferent heat exchanger systems, but all operate together within a PHESsystem, such as PHES system 1000, to provide the desired operatingconditions for operational modes. Each heat exchanger system consists ofone or more heat exchanger units that may be connected via manifoldsand/or other fluid routing systems.

The main heat exchanger system 300A has two major modes of operation,mirroring the PHES system main modes of operation. During PHES systemgeneration (e.g., generation 1004 in FIG. 10 ), the heat exchangersoperate in a forward flow direction at a flow rate between a maximumpower (operational maximum) mass flow rate and a maximum turndown(operational minimum) mass flow rate. In this generation mode, heat istransferred from an HTS medium to a working fluid at HHX system 500,from the working fluid to a CTS medium at CHX system 600, from alow-pressure working fluid stream to a high-pressure working fluidstream at RHX system 400, and from the working fluid to the ambientenvironment or other heat sink at AHX system 700. During PHES systemcharge (e.g., charge 1002 in FIG. 10 ), the heat exchangers operate inthe reverse flow direction at a flow rate between the maximum power massflow rate and the maximum turndown mass flow rate. In this process, heatis transferred from the working fluid to the HTS medium at HHX system500, from the CTS medium to the working fluid at CHX system 600, andfrom a high-pressure working fluid stream to a low-pressure workingfluid stream at RHX system 400.

Under some PHES system modes, such as a long term Cold Dry Standby 1010(see FIG. 10 ), the HTS medium and the CTS medium in the main heatexchanger system 300A is drained to thermal reservoirs (e.g., CTS system691 and/or 692, and/or HTS system 591 and/or 592). In such a scenario,heat traces may be used to ensure that the HTS medium does not freeze.

Main heat exchanger system 300A includes CHX system 600. A function ofCHX system 600 is to transfer heat between a CTS medium and a workingfluid. As illustrated in FIGS. 6A and 6B, embodiments of CHX system 600can include differing amounts of cold-side heat exchangers (“CHX”)depending on design requirements. CHX system 600 is illustrated asincluding cold-side heat exchangers 600-1, 600-2, through 600-n, whichreflect in these example embodiments 390, 391 at least three CHX and caninclude more than three CHX, although other PHES system embodiments mayhave less than three CHX. In some embodiments, as illustrated in FIGS.6A and 6B, each of CHX 600-1 through 600-n is a cross-flow heatexchanger. Specifically, a CTS medium flows through each of CHX 600-1through 600-n between fluid interconnect 1 and fluid interconnect 13.Additionally, a working fluid flows through each of CHX 600-1 through600-n between fluid interconnect 2 and fluid interconnect 14. In anotherembodiment, one or more CHX may not be cross-flow, and may have anotherinternal fluid routing arrangement; however, CTS flow betweeninterconnects 1, 13 and working fluid flow between interconnects 2, 14is maintained.

As illustrated in FIGS. 6A and 6B, each of CHX 600-1 through 600-n isconnected in parallel to the CTS medium and working fluid flows,respectively, with respect to each other CHX. In another embodiment, oneor more CHX may be connected in series with one or more CHX. In anotherembodiment, one more groups of CHX may be connected in parallel, and oneor more groups of CHX may be connected in series. In another embodiment,individual CHX and/or groups of CHX may be combined in variouscombinations of series and parallel configurations.

Main heat exchanger system 300A includes HHX system 500. A function ofHHX system 500 is to transfer heat between an HTS medium and a workingfluid. Embodiments of HHX system 500 can include differing amounts ofhot-side heat exchangers (“HHX”) depending on design requirements. HHXsystem 500 is illustrated as including hot-side heat exchangers 500-1,500-2, through 500-n, which reflect in these example embodiments 390,391 at least three HHX and can include more than three HHX, althoughother PHES system embodiments may have less than three HHX. In someembodiments, as illustrated in FIGS. 6A and 6B, each of HHX 500-1through 500-n is a cross-flow heat exchanger. Specifically, an HTSmedium flows through each of HHX 500-1 through 500-n between fluidinterconnect 6 and fluid interconnect 8. Additionally, a working fluidflows through each of HHX 500-1 through 500-n between fluid interconnect7 and fluid interconnect 9. In another embodiment, one or more HHX maynot be cross-flow, and may have another internal fluid routingarrangement; however, HTS flow between interconnects 6, 8 and workingfluid flow between interconnects 7, 9 is maintained.

As illustrated in FIGS. 6A and 6B, each of HHX 500-1 through 500-n isconnected in parallel to the HTS medium and working fluid flows,respectively, with respect to each other HHX. In another embodiments,one or more HHX may be connected in series with one or more HHX. Inanother embodiments, one more groups of HHX may be connected inparallel, and one or more groups of HHX may be connected in series. Inanother embodiment, individual HHX and/or groups of HHX may be combinedin various combinations of series and parallel configurations.

Main heat exchanger system 300A includes RHX system 400. A function ofRHX system 400 is to transfer heat between a high-pressure working fluidstream and a low-pressure working fluid stream. Embodiments of RHXsystem 400 can include differing amounts of recuperator heat exchangers(“RHX”) depending on design requirements. In FIGS. 6A and 6B, RHX system400 is illustrated as including recuperator heat exchangers 400-1,400-2, through 400-n, which reflect at least three RHX and can includemore than three RHX in these example embodiments, 390, 391 althoughother PHES system embodiments may have less than three RHX. In someembodiments, as illustrated in FIGS. 6A and 6B, each of RHX 400-1through 400-n is a cross-flow heat exchanger. Specifically, workingflows through each of RHX 400-1 through 400-n between fluid interconnect5 and fluid interconnect 11. Additionally, the working fluid in adifferent part of the working fluid loop flows through each of RHX 400-1through 400-n between fluid interconnect 10 and fluid interconnect 12.In another embodiment, one or more RHX may not be cross-flow, and mayhave another internal fluid routing arrangement; however, working fluidflow between interconnects 5, 11 and working fluid flow betweeninterconnects 10, 12 is maintained.

As illustrated in FIGS. 6A and 6B, each of RHX 400-1 through 400-n isconnected in parallel to the working fluid flows with respect to eachother RHX. In another embodiments, one or more RHX may be connected inseries with one or more RHX. In another embodiments, one more groups ofRHX may be connected in parallel, and one or more groups of RHX may beconnected in series. In another embodiment, individual RHX and/or groupsof RHX may be combined in various combinations of series and parallelconfigurations.

Main heat exchanger system 300A includes AHX system 700. A function ofAHX system 700 is to transfer heat from a working fluid to the ambientenvironment, or other external heat sink, during generation mode. In oneembodiment, the AHX system 700 will only be operational during PHESsystem generation (e.g., generation 1004 in FIG. 10 ). For example,during PHES system charge (e.g., charge 1002 in FIG. 10 ), the AHXsystem 700 will be bypassed, as further discussed herein.

Embodiments of AHX system 700 can include differing configurations andamounts of ambient heat exchangers (“AHX”) (also referred to as ambientcoolers) depending on design requirements. In embodiment 390 in FIG. 6A,AHX system 700 is illustrated as including ambient heat exchangers700-1, 700-2, through 700-n, which reflect at least three AHX in thisexample embodiment and can include more than three AHX, although otherPHES system embodiments may have less than three AHX. In a preferredembodiment, AHX system 700 includes only one AHX, e.g., AHX 700-1. Inembodiment 390, as illustrated in FIG. 6A, each of AHX 700-1 through700-n is an ambient cooler that exhausts heat to the environment fromthe working fluid flowing through the AHX between fluid interconnects 4and 3. In the embodiment of FIG. 6A, fluid interconnects 28, 29 are notutilized. In the embodiment of FIG. 6A, individual AHX may include oneor more variable-speed fans that can be controlled to adjust ambient airflow across the AHX in order to reach a desired working fluid outlettemperature of the AHX system 700. As illustrated in FIG. 6A, each ofAHX 700-1 through 700-n is connected in parallel to the working fluidflow with respect to each other AHX. In another embodiments, one or moreAHX may be connected in series with one or more AHX. In anotherembodiments, one more groups of AHX may be connected in parallel, andone or more groups of AHX may be connected in series. In anotherembodiment, individual AHX and/or groups of AHX may be combined invarious combinations of series and parallel configurations.

In embodiment 391 in FIG. 6B, AHX system 700 is illustrated as includingambient heat exchangers 701-1, 701-2, through 701-n, which reflect atleast three AHX in this example embodiment and can include more thanthree AHX, although other PHES system embodiments may have less thanthree AHX. In a preferred embodiment, AHX system 700 includes only oneAHX, e.g., AHX 701-1. In embodiment 391, as illustrated in FIG. 6B, eachof AHX 701-1 through 701-n is a cross-flow heat exchanger. Specifically,a heat sink fluid flows through each of AHX 701-1 through 701-n betweenfluid interconnect 28 and fluid interconnect 29. Additionally, a workingfluid flows through each of AHX 701-1 through 701-n between fluidinterconnect 4 and fluid interconnect 3. In the embodiment of FIG. 6B,the heat sink fluid may be ambient air that is pulled from and/or isexhausted to the environment, or the heat sink fluid may be a fluid thatis pulled from a heat sink fluid reservoir (not shown) and/or sent toheat sink fluid reservoir (not shown) or other heat sink (not shown),such as a thermal waste heat capture/transfer system. In embodiment 391of FIG. 6B, heat sink fluid mass flow rate through the AHXs may beadjusted in order to reach a desired working fluid outlet temperature ofthe AHX system 700. As illustrated in FIG. 6B, each of AHX 701-1 through701-n is connected in parallel to the working fluid flow with respect toeach other AHX. In another embodiments, one or more AHX may be connectedin series with one or more AHX. In another embodiments, one more groupsof AHX may be connected in parallel, and one or more groups of AHX maybe connected in series. In another embodiment, individual AHX and/orgroups of AHX may be combined in various combinations of series andparallel configurations.

Main heat exchanger system 300A, as illustrated in embodiment 390 and391 in FIGS. 6A and 6B, may include heat traces 460 and 560 as part ofthe RHX system 400 and HHX system 500, respectively. A function of heattrace 460 is to maintain fluid manifolds and/or other metal mass atdesired setpoint temperatures during various modes and/or states, forexample, in order to reduce thermal gradients on sensitive components. Afunction of heat trace 560 is to maintain fluid manifolds and/or othermetal mass at desired setpoint temperatures during various modes and/orstates, for example, in order to avoid freezing (i.e., phase change) ofHTX medium in the HHX system 500 and/or to reduce thermal gradients onsensitive components. Each of the heat traces 460 and 560 can functionto reduce thermal ramp rates, which benefits heat exchanger longevity,and allows for faster PHES system 1000 startup times. Heat traces 460and 560 are illustrated as near fluid interconnects 12 and 9,respectively. However, heat traces 460 and 560 can be located at otherlocations within RHX system 400 and HHX system 500 in order toaccomplish their functions. Additionally or alternatively, heat traces460 and 560 can include heat traces at multiple locations within RHXsystem 400 and HHX system 500 in order to accomplish their functions.

E. Working Fluid Loop Subsystem

FIG. 3 is a schematic fluid path diagram of a working fluid loop 300which may be implemented in a PHES system, such as PHES system 1000,according to an example embodiment. FIG. 3 provides additional detailconcerning working fluid loop 300 than is shown in the top-levelschematic of FIG. 2 . In general terms, the working fluid loop 300includes, for example, high-pressure fluid paths and low-pressure fluidpaths separated by the turbomachinery, turbomachinery bypass andrecirculation loops, heat exchangers (e.g., excess heat radiators),valves, pressure relief devices, working fluid supply components (e.g.,working fluid compressor), an inventory control system including workingfluid tank systems (e.g., high pressure tank systems and low pressuretank systems), and sensors for pressure, temperature, flow rate,dewpoint, speed, and/or fluid concentration. Other embodiments of aworking fluid loop operable in PHES systems disclosed herein arepossible as well.

FIG. 3N and FIG. 3O illustrate circulatory flow paths of working fluidin working fluid loop 300 for charge mode 1002 and generation mode 1004,respectively. Bold fluid paths illustrate the circulatory flow paths andarrows on bold fluid paths indicate circulatory flow direction. Workingfluid may be resident in other fluid paths, but is not activelycirculating because such other fluid paths do not form a circulatorycircuit with an inlet and outlet (i.e., they are a dead end). Valvepositions are indicated with a filled valve icon representing a closedvalve, an unfilled valve icon representing an open valve, and across-hatched valve representing a valve that may change position statewithout affecting the illustrated circulatory flow path. For example, inFIG. 3N, valve 231 is closed, valve 131 is open, and valve 242 maychange position state without affecting the flow path.

The embodiment of working fluid loop 300 illustrated in FIG. 3 can servenumerous roles within PHES system 1000. The working fluid loop 300 canroute working fluid between the turbomachinery and the heat exchangers.The working fluid loop 300 can provide working fluid to the main heatexchanger system 300A for transferring heat between HTS medium and CTSmedium during, for example, charge or generation cycles. The workingfluid loop 300 can protect the turbomachinery during emergency tripevents, and help with compressor surge prevention and overpressureprevention. The working fluid loop 300 can maintain its pressures (e.g.,pressures in low-pressure and high-pressure fluid paths) below specifiedset points for each mode of PHES system operation. The working fluidloop 300 can help with smooth PHES system 1000 startup and shutdown,including, for example, working fluid bypass flow during generationcycle startup to prevent bidirectional loads/demands on a VFD. Theworking fluid loop 300 can quickly bring working fluid pressures down toallow mode switching operation within short time intervals. The workingfluid loop 300 can maintain working fluid loop pressures at or above aminimum working fluid loop base pressure, such as whenever CHX system600 or HHX system 500 are filled with their respective CTS or HTS media,for example, to prevent leakage of CTS or HTS media into the workingfluid loop 300. The working fluid loop 300 can adjust low-side pressurein the working fluid loop between a minimum pressure and workingpressures (i.e. pressures during charge and generation), as a means ofcontrolling PHES system power. The working fluid loop 300 can regulatecirculate working fluid mass, for example to control PHES systempressures, PHES system power, and/or compensate for working fluid lossesfrom the working fluid loop over time.

The following paragraphs describe components of the working fluid loop300:

Pressure relief device 101 is a pressure relief device on a low-pressurelow-temperature (“LPLT”) portion of the working fluid loop 300. Itprotects from overpressure the LPLT portion of the working fluid loop inthe vicinity, for example, where high-pressure working fluid could beintroduced through the turbomachinery, recirculation valves, or bypassvalves.

Pressure relief device 102 is a pressure relief device on a low-pressuremedium-temperature (“LPMT”) portion of the working fluid loop 300. Itprotects from overpressure the LPMT portion of the working fluid loop300 in the vicinity, for example, where high-pressure working fluidcould be introduced through the turbomachinery, recirculation valves,and/or bypass valves.

Valve 119 regulates a high-flow recirculation fluid path aroundcompressor system 130 that can be opened, for example, to reduce and/orprevent surge in charge compressor system 130. For example, valve 119may be opened following a trip event during charge mode operation orwhen valve 131 is closed. In an embodiment where valve 132 issufficiently large, valve 119 can be omitted.

Valve 131 is a charge compressor system 130 shutoff valve that, whenclosed, isolates charge compressor system 130 from the high-pressureside of the working fluid loop 300, for example, during generation modeor following a trip event. Valve 131 preferably fails closed. A benefitof valve 131 is that it can be closed to isolate the compressor system130 from the large, high-pressure working fluid volume that is presentin fluid paths on the side of valve 131 opposite the compressor system130. That large volume could cause the compressor system 130 (e.g.compressor 130-1) to surge if the compressor system 130 (e.g. compressor130-1) were to spin down following a power loss or unexpected tripscenario in the PHES system 1000.

Valve 132 regulates a recirculation fluid path around compressor system130 that can be opened, for example, to recirculate working fluid drivenby charge compressor system 130 during, for example, cooldown (e.g.,during slow rolling) or after a mode switch. Valve 132 may exhibit slowresponse time and preferably fails open. A benefit of failing open isthat a valve failure does not prevent compressor system 130 cooldown,which is beneficial to prevent damage to the compressor system 130.

Heat exchanger 132H is a radiator in the recirculation fluid pathregulated by valve 132 and removes heat (e.g., to ambient) from theworking fluid recirculating through charge compressor system 130, forexample, following the end of charge mode operation.

Valve 133 is a working fluid dump valve located downstream of the chargecompressor system 130 and isolation valve 131. Valve 133 may be, forexample, used to reduce the working fluid pressure in the vicinity ofthe outlet of compressor 130 during certain events, for example tripevents during charge mode 1002. Opening valve 133 dumps working fluid toambient, or a working fluid reservoir (not shown), and decreases workingfluid pressure in the vicinity of the outlet of compressor 130, whichbeneficially reduces the risk of compressor system 130 surge.

Valve 141 is a charge turbine system 140 shutoff valve that, whenclosed, isolates charge turbine system 140 from the high-pressure sideof the working fluid loop 300, for example, during generation mode orfollowing a trip event. Valve 141 preferably fails closed. A benefit ofvalve 141 is that it can be closed, in conjunction with closing valve131, to prevent working fluid mass moving from the high-pressure side ofthe main working fluid loop 300 to the low-pressure side of the workingfluid loop 300, which could result in the working fluid loop 300equilibrating in pressure to a settle-out pressure greater than thepressure rating of components in the low-pressure side of the loop.

Valve 142 regulates a recirculation fluid path around charge turbinesystem 140 that can be opened, for example, to recirculate working fluidthrough turbine system 140 during, for example, turning (e.g., slowrolling) or after a mode switch. Valve 142 may exhibit slow responsetime and preferably fails open. A benefit of valve 142 is that it can beopened to prevent the inlet pressure of the charge turbine system 140from dropping substantially below the outlet pressure of the turbinesystem 140 upon closing valve 141, which is beneficial because itprevents the turbine system 140 from operating outside typical designspecifications for pressure differentials.

Fan 142F can be operated, when valve 142 is open, to providerecirculation flow of working fluid through the turbine 140 via therecirculation loop controlled by valve 142. This is beneficial, forexample, when the spinning turbine system 140 does not createappreciable working fluid flow through the turbine system 140 andconsequently experiences windage. Fan 142 can be turned on to createworking fluid flow through the turbine system 140 via the recirculationloop to alleviate the windage.

Valve 222 regulates a bypass fluid path that can be opened, for exampleduring generation mode, to provide a working fluid bypass path aroundthe high-pressure side of RHX system 400 and HHX system 500, therebyallowing some amount of working fluid flow through the bypass fluid pathinstead of through RHX system 400 and HHX system 500. Opening valve 222,preferably in conjunction with closing valves 231 and 241, removesenergy (in the form of hot compressed working fluid) that is supplied tothe turbine system 240, thereby starving turbine system 240.Beneficially, valve 222 can be opened, for example, when the GPT system200 experiences a loss of load event (e.g., from the electric grid) or atrip event. Closing valves 231 and 241 and opening of 222 collectivelycan prevent overspeed of the GPT system 200 as a result of turbinesystem 240 overspeed.

Valve 229 regulates a bypass fluid path that can be opened to provide ahigh-flow working fluid bypass path around the high-pressure side of RHXsystem 400, HHX system 500, and turbine system 240, thereby allowingsome amount of working fluid flow through the bypass fluid path insteadof through RHX system 400, HHX system 500, and turbine system 240.Beneficially, valve 229 can be opened to reduce load during startup ofgeneration mode and to prevent generation turbine system 240 fromgenerating substantial power during startup of generation mode. Openingvalve 229 reduces a net load required of the generator system 210 (e.g.,generator 210-1 acting as a motor) during generation mode startup.Opening valve 229 reduces the compressor system 230 power need byreducing outlet pressure at the compressor system 230. Opening valve 229also starves the turbine system 240 of much of its fluid flow so thatthe turbine system 240 does not produce substantially more power thanthe compressor system 230. By keeping a low, but net positive,electrical power demand from generator system 210 (e.g., generator 210-1acting as a motor) means that a VFD (e.g., VFD 214) supplying power tothe generator system 210 can maintain speed control duringstartup/spin-up. Opening valve 229 also provides a high-flow fluid pathto prevent surge in compressor system 230, for example, following a tripevent out of generation mode operation and when valve 231 is closed.

Valve 231 is a generation compressor system 230 shutoff valve that, whenclosed, isolates generation compressor system 230 from the high-pressureside of the working fluid loop during charge mode operation or followinga trip event. Valve 231 preferably fails closed. A benefit of valve 231is that it can be closed to isolate the compressor system 230 from thelarge high-pressure working fluid volume that is present in fluid pathson the side of valve 231 opposite the compressor system 230. That largevolume could cause the compressor system 230 (e.g. compressor 230-1) tosurge if the compressor system 230 (e.g. compressor 230-1) were to spindown following a power loss or unexpected trip scenario in the PHESsystem 1000.

Valve 232 regulates a recirculation fluid path around generationcompressor system 230 that can be opened, for example, to recirculateworking fluid driven by generation compressor system 230 during, forexample, turning or after a mode switch. Valve 232 may exhibit slowresponse time and preferably fails open. A benefit of valve 232 failingopen is that it allows for turbomachinery temperature equilibration uponfailure; for example, failure during a during a post-shutdown spinningmode allows cooldown of hot portions of the compressor system 230 andwarmup of the inlet side of the compressor system 230.

Valve 241 is generation turbine system 240 shutoff valve that, whenclosed, isolates generation turbine system 240 from the high-pressureside of the working fluid loop 300 during, for example, charge modeoperation or following a trip event. In practical effect, closing valve241 can starve turbine system 240 and prevent GPT system 200 overspeed.Valve 241 preferably fails closed. A benefit of valve 241 is that can beclosed to isolate a source of high-pressure working fluid that couldcontinue to drive the turbine system 240 during, for example, aloss-of-grid-load event, which otherwise might cause an overspeed eventfor the GPT system 200.

Valve 242 regulates a recirculation fluid path around generation turbinesystem 240 that can be opened, for example, to recirculate working fluidthrough turbine system 240 during, for example, cooldown (e.g. duringslow rolling) or after a mode switch. Valve 242 may exhibit slowresponse time and preferably fails open. A benefit of valve 242 failingopen is that if valve 242 fails, by failing open it allows for cooldownspinning of GPT system 200 after shutdown of GPT system 200. Cooldownspinning can prevent bowing of rotating components in theturbomachinery. Another benefit of valve 242 failing open is that, whenfailed open, GPT system 200 can continue to function during generation(e.g., mode 1004) or slow turning (e.g., mode 1006), albeit withdecreased efficiency during generation due to open valve 242 creating ableed path for the working fluid.

Heat exchanger 242H is a radiator in the recirculation fluid pathregulated by valve 242 and removes heat (e.g., to ambient) from theworking fluid recirculating through turbine system 240.

Fan 242F can be operated, when valve 142 is open, to providerecirculation flow of working fluid through the turbine 240 via therecirculation loop controlled by valve 242. This is beneficial, forexample, when the spinning turbine system 240 does not createappreciable working fluid flow through the turbine system 240 andconsequently experiences windage. Fan 242 can be turned on to createworking fluid flow through the turbine system 240 via the recirculationloop to alleviate the windage and/or for cooling down of turbine system240 during, for example, slow rolling.

Valve 323 regulates a bypass fluid path that can be opened, for exampleduring charge mode, to provide a working fluid bypass path around AHXsystem 700, thereby allowing some amount of working fluid flow throughthe bypass fluid path instead of through AHX system 700. Beneficially,opening valve 323, preferably in conjunction with closing valve 324 (andvalve 325 if present), diverts working fluid around AHX system 700,thereby reducing working fluid loop 300 pressure drop when heat dumpfrom the working fluid is not desired, such as during charge modeoperation. Valve 323 may exhibit slow actuation time and preferablyfails open. Beneficially, valve 323 preferably fails open so thatworking fluid loop 300 can maintain flow if working fluid valve 324 (andvalve 325 if present) is closed or were to fail closed. If valve 323 andvalve 324 (or valve 325 if present) are both closed, working fluidcirculation in the working fluid loop 300 would stop and the loss ofworking fluid flow could damage turbomachinery attempting to circulatethe working fluid. Additionally, if valve 323 fails open, it allows thePHES system 1000 to continue operating, albeit with a loss of efficiencyin some modes. In an alternative embodiment of a working fluid loop,valve 323 may be combined with valve 324, at the junction of the fluidpath exiting interconnect 5 and the fluid path entering interconnect 4in generation mode, as a two-position, three-way valve to accomplish thesame effect as the two valves 323, 324.

Valve 324 is an isolation valve that, when closed, isolates AHX system700 from circulation of working fluid through AHX system 700, forexample during charge mode. If valve 325 is present, both valves 324 and325 may be closed to completely isolate AHX system 700 from workingfluid, for example during charge mode and/or service. Valve 324 mayexhibit slow actuation time and preferably fails to current position oralternately fails open. Beneficially, if valve 324 fails to currentposition, the PHES system 1000 can continue its current operation.Alternatively, valve 324 can be specified to fail open for the reasonsdescribed above with respect to valve 323.

Valve 325 is an isolation valve that, when closed, isolates AHX system700 from circulation of working fluid through AHX system 700, forexample during charge mode. Valve 325 may exhibit slow actuation timeand preferably fails to current position. Beneficially, if valve 325fails to current position, the PHES system 1000 can continue its currentoperation. In an alternative embodiment, valve 325 may be omitted fromworking fluid loop 300. FIGS. 3K, 3L and their corresponding disclosureillustrate that embodiment. In this alternate embodiment with valve 325omitted, closing valve 324 and opening valve 323 will cause workingfluid to not circulate through AHX system 700, and instead bypass AHXsystem 700 through valve 323. However, omitting valve 325 means that AHXsystem 700 cannot be fully isolated from the working fluid loop 300, asit will see resident working fluid.

Filter 301 is a working fluid filter (or pre-filter) for working fluidcompressor 303 that provides filtration of working fluid entering theworking fluid loop 300 from an outside source, such as ambient air whenair is the working fluid or for a working fluid that is stored in anoutside working fluid make-up reservoir (not shown). Filter 301 may actas a pre-filter if working fluid compressor 303 also contains filters.

Valve 302 is a working fluid compressor 303 feed valve that, whenopened, provides the ability for the working fluid compressor 303 topull working fluid from ambient or an outside working fluid make-upreservoir (not shown). When closed, valve 302 provides the ability forthe working fluid compressor 303 to pull working fluid from the workingfluid loop 300 (e.g., from evacuation lines via the fluid paths throughvalve 304 or valve 305).

Working fluid compressor 303 is a make-up working fluid compressor. Whenactivated, working fluid compressor 303 can, depending on valve states,provide working fluid for inventory control system (“ICS”) 300B storagetank systems 310 and/or 320. Additionally or alternatively, whenactivated, working fluid compressor 303 can, depending on valve states,replenish working fluid loop 300 with working fluid lost through leakageor venting. Additionally or alternatively, when activated, working fluidcompressor 303 can, depending on valve states, evacuate working fluidloop 300 to reduce pressure below what ICS 300B valve arrangements canaccomplish when lowering the working fluid loop 300 pressure below thesettle-out pressure for startup. This is beneficial because workingfluid loop 300 is preferably partially evacuated in order to dropworking fluid loop 300 pressure when one powertrain (e.g., CPT system100 or GPT system 200) has spun down and the other power train isspinning up. For example, if PHES system 1000 is coming out of chargemode 1002 and CPT system 100 has just spun down, it is desirable tolower the working fluid loop 300 pressure so that GPT system 200 canstart to spin up. “Settle-out” pressure can be interpreted as theresulting pressure in the working fluid loop 300 if working fluid masswere allowed to move from the high-pressure side of the working fluidloop 300 to the low-pressure side of the working fluid loop 300 to thepoint where the pressure on both sides equilibrated. Additionally oralternatively, when activated, working fluid compressor 303 can,depending on valve states, counteract hysteresis in the functioning ofICS 300B by pumping working fluid mass from the low-pressure side of theworking fluid loop 300 to high-pressure tank system 320.

Valve 304 is a feed valve for the working fluid compressor 303 on alow-pressure-side evacuation fluid path of working fluid loop 300. Valve304, when open, connects the low-pressure side of working fluid loop 300to working fluid compressor 303 for pulling working fluid from workingfluid loop 300 into ICS 300B high-pressure tank system 320.

Valve 305 is a feed valve for the working fluid compressor 303 on ahigh-pressure-side evacuation fluid path of working fluid loop 300.Valve 305, when open, connects the high-pressure side of working fluidloop 300 to working fluid compressor 303 for pulling working fluid fromworking fluid loop 300 into ICS 300B high-pressure tank system 320.

Valve 308 is an evacuation valve on the low-pressure side of workingfluid loop 300. Valve 308, when open, allows working fluid in theworking fluid loop 300 to be evacuated to the environment or an outsideworking fluid make-up reservoir (not shown). Valve 308 is primarily forservicing of working fluid loop 300, but can also be used for inventorycontrol purposes (e.g., reducing working fluid mass in working fluidloop 300) related to power generation mode 1004, charge mode 1002, orother operations.

Pressure relief device 309 is an ICS 300B low-pressure-side pressurerelief device that protects low-pressure fluid paths in working fluidloop 300 from over pressurization, for example, near where high-pressureworking fluid is introduced by ICS 300B (e.g., via valve 322) into thelow-pressure fluid paths.

Low-pressure tank system 310 is an ICS 300B tank system that includesone or more tanks that store working fluid at low pressure (e.g., lessthan the pressure in high-pressure tank system 320, and/or less than thepressure in the high-pressure side of working fluid loop 300). Workingfluid may be moved into low-pressure tank system 310 from, for example,working fluid loop 300. Working fluid may be released from low-pressuretank system 310 into, for example, working fluid loop 300. Preferably,tank system 310 includes built-in pressure relief devices.

Valve 311 is an ICS 300B HP-LP valve that, for example, when open,allows for release of high-pressure working fluid from the high-pressureside of working fluid loop 300 into the low-pressure tank system 310.Valve 311 may be a controlled proportional valve that is used, forexample, for controlling PHES system 1000 power ramping rates.

Valve 312 is an ICS 300B LP-LP valve that, for example, when open,allows for movement of low-pressure working fluid between low-pressuretank system 310 and the low-pressure side of working fluid loop 300.

Valve 314 is an evacuation valve on the high-pressure side of workingfluid loop 300. Valve 314, when open, allows working fluid in theworking fluid loop 300 to be evacuated to the environment or an outsideworking fluid make-up reservoir (not shown). Valve 314 is primarily forservicing of working fluid loop 300, but can also be used for inventorycontrol purposes (e.g., reducing working fluid mass in working fluidloop 300) related to power generation mode 1004, charge mode 1002, orother operations.

Valve 318 is a dump valve on the high-pressure side of working fluidloop 300. Valve 318, when open, allows working fluid in thehigh-pressure side of the working fluid loop 300 to be dumped to the ICS300B low-pressure tank system 310, lowering pressure in the workingfluid loop 300. Beneficially, this preserves filtered working fluid asopposed to evacuating working fluid through valves 308 or 314. Thoughsimilarly arranged in ICS 300B, valve 318 may differ from valve 311.Valve 318 may be a fast switched (i.e., “bang-bang”) valve and/or may belarger than valve 318. This is beneficial for moving high-pressureworking fluid from the working fluid loop 300 into the low-pressure tanksystem 310 at a much faster rate than valve 311 can accomplish, whichmay be preferred for certain mode transitions or trip events.

Pressure relief device 319 is an ICS 300B high-pressure-side pressurerelief device that protects high-pressure fluid paths in working fluidloop 300 from over pressurization.

High-pressure tank system 320 is an ICS 300B tank system that includesone or more tanks that store working fluid at high pressure (e.g.,higher than the pressure in low-pressure tank system 310, and/or higherthan the pressure in the low-pressure side of working fluid loop 300).Working fluid may be moved into high-pressure tank system 320 from, forexample, the high-pressure side of working fluid loop 300 via ICS 300Bvalves (e.g., valve 321) and/or working fluid compressor 303. Workingfluid may be released from high-pressure tank system 320 into, forexample, the low-pressure side of working fluid loop 300 via ICS 300Bvalves (e.g., valve 322). Preferably, the high-pressure tank system 320includes built-in pressure relief devices.

Valve 321 is an ICS 300B HP-HP valve that, for example, when open,allows for movement of high-pressure working fluid between thehigh-pressure side of working fluid loop 300 and high-pressure tanksystem 320.

Valve 322 is an ICS 300B LP-HP valve that, for example, when open,allows for release of high-pressure working fluid from high-pressuretank system 320 into the low-pressure side of working fluid loop 300.

Sensors 119S, 130S, 131S, 132S, 140S, 141S, 142S, 229S, 230S, 231S,232S, 240S, 241S, 242S, 324S, 325S, 361S, 362S, 363S, 364S, 365S, 366S,and 367S are monitoring and reporting devices that can provide one ormore of pressure, temperature, flow rate, dewpoint, and/or fluidconcentration data to one or more control systems controlling and/ormonitoring conditions of the PHES system 1000.

Sensor 303S is a monitoring and reporting devices that can provide oneor more of compressor speed, pressure, temperature, and/or flow ratedata to one or more control systems controlling and/or monitoringconditions of the PHES system 1000.

Sensors 310S and 320S are monitoring and reporting devices that canprovide one or more of pressure, temperature, dewpoint, and/or fluidconcentration data to one or more control systems controlling and/ormonitoring conditions of the PHES system 1000.

Valve 401 regulates a bypass fluid path that can be opened, for exampleduring generation mode, to provide a working fluid bypass path aroundthe low-pressure side of RHX system 400 and AHX system 700, therebyallowing some amount of working fluid flow through the bypass fluid pathinstead of through RHX system 400 and AHX system 700. Beneficially,valve 401 may be used in conjunction with valve 222, 323, 324 (and 325,if present) to mitigate a negative effect of opening valve 222. During,for example, generation mode 1004, opening valve 222 (with valves 231,241 closed), will cause the outlet temperature of turbine system 240 todrop quickly. That results in circulation of colder working fluiddownstream of the turbine system 240 that could shock (and potentiallydamage) the downstream RHX system 400 and AHX system 700 if the colderworking fluid were allowed to pass into those heat exchangers.Therefore, as an example, when valve 222 is opened, valve 401 may alsobe opened and preferably valves 323, 324 (and 325, if present) may beclosed, so that the colder working fluid flow from the turbine system240 outlet bypasses around RHX system 400 and AHX system 700 and flowsinstead to the inlet of the CHX system 600, which is expecting colderworking fluid.

HP/LP Working Fluid Paths

In working fluid loop 300, high-pressure fluid paths are downstream ofcharge and generation compressor systems 130, 230 and upstream of chargeand generation turbine systems 140, 240 (i.e., between outlets of chargeand generation compressor systems 130, 230 and inlets of charge andgeneration turbine systems 140, 240, respectively). Low-pressure fluidpaths are downstream of charge and generation turbine systems 140, 240and upstream of charge and generation compressor systems 130, 230 (i.e.,between outlets of charge and generation turbine systems 140, 240 andinlets of charge and generation compressor systems 130, 230,respectively).

For example, a high-pressure fluid path is between the CPT system 100compressor system 130 outlet and the CPT turbine system 140 inlet. InFIGS. 3 and 3N, that high-pressure fluid path encompasses fluidinterconnects 17, 7, 9, 10, 12, and 18. With reference to thecirculatory flow paths illustrated in bold in FIG. 3N, the portion ofthis high-pressure fluid path downstream of compressor system 130,encompassing fluid interconnects 17, 7, 9, 10, and ending at RHX system400 can additionally be considered a high-pressure high-temperature(e.g., HP-HT) fluid path. Similarly, the portion of this high-pressurefluid path downstream of RHX system 400, encompassing fluidinterconnects 12, 18, and ending at the inlet to turbine system 140 canadditionally be considered a high-pressure medium-temperature (e.g.,HP-MT) fluid path.

Another high-pressure fluid path is between the GPT system 200compressor system 230 outlet and the GPT turbine system 240 inlet. InFIGS. 3 and 3O, that high-pressure fluid path encompasses fluidinterconnects 22, 12, 10, 9, 7, and 23. With reference to thecirculatory flow paths illustrated in bold in FIG. 3O, the portion ofthis high-pressure fluid path downstream of compressor system 230,encompassing fluid interconnects 22, 12, and ending at RHX system 400can additionally be considered a high-pressure medium-temperature (e.g.,HP-MT) fluid path. Similarly, the portion of this high-pressure fluidpath downstream of RHX system 400, encompassing fluid interconnects 10,9, 7, 23, and ending at the inlet to turbine system 240 can additionallybe considered a high-pressure high-temperature (e.g., HP-HT) fluid path.

As another example, a low-pressure fluid path is between the CPT system100 turbine system 140 outlet and the CPT compressor system 130 inlet.In FIGS. 3 and 3N, that low-pressure fluid path encompasses fluidinterconnects 19, 14, 2, 5, 11, and 20. With reference to thecirculatory flow paths illustrated in bold in FIG. 3N, the portion ofthis low-pressure fluid path downstream of turbine system 140,encompassing fluid interconnects 19, 14, 2, 5, and ending at RHX system400 can additionally be considered a low-pressure low-temperature (e.g.,LP-LT) fluid path. Similarly, the portion of this low-pressure fluidpath downstream of RHX system 400, encompassing fluid interconnects 11,20, and ending at the inlet to compressor system 130 can additionally beconsidered a low-pressure low-temperature (e.g., LP-LT) fluid path.

Another low-pressure fluid path is between the GPT system 200 turbinesystem 240 outlet and the compressor system 230 inlet. In FIGS. 3 and3O, that low-pressure fluid path encompasses fluid interconnects 25, 11,5, 4 and 3 (depending on AHX system 700 bypass state), 2, 14, and 26.With reference to the circulatory flow paths illustrated in bold in FIG.3O, the portion of this low-pressure fluid path downstream of turbinesystem 240, encompassing fluid interconnects 25, 11, and ending at RHXsystem 400 can additionally be considered a low-pressuremedium-temperature (e.g., LP-MT) fluid path. Similarly, the portion ofthis low-pressure fluid path downstream of RHX system 400, encompassingfluid interconnects 5, 4 and 3 (depending on AHX system 700 bypassstate), 2, 14, 26, and ending at the inlet to compressor system 230 canadditionally be considered a low-pressure medium-temperature (e.g.,LP-MT) fluid path.

Powertrain Isolation

Valve 131 and valve 141 may be closed to isolate the CPT system 100turbomachinery during generation mode 1004. Valve 231 and valve 241 maybe closed to isolate the GPT system 200 turbomachinery during chargemode 1002. As noted above, these isolation valves 131, 141, 231, 241 arepreferably fail-closed valves and preferably they can close quickly tohelp protect the turbomachinery during a trip event.

AHX System Isolation

The AHX system 700 can exhaust excess heat in the working fluid to theenvironment. In some embodiments, excess heat may be rejected from thePHES system 1000 via the working fluid loop 300 only during generation(e.g., mode 1004). Excess heat from inefficiency is generated duringboth charge (e.g. mode 1002) and generation (e.g., mode 1004) due toinefficiencies of the turbomachinery. In an embodiment where excess heatis not rejected during a charge mode (e.g., mode 1002), the excess heataccumulates and results in, for example, a higher CTS medium 690temperature. In an embodiment where excess heat is rejected during ageneration mode (e.g., mode 1004), excess heat from charge modeinefficiency and generation mode inefficiency can be removed from theworking fluid loop 300 through the AHX system 700.

Consequently, in a preferred embodiment, it is desirable to provide amode-switchable working fluid heat dissipation system that can beactivated during generation mode 1004 and bypassed during charge mode1002, or vice versa in another embodiment. In working fluid loop 300, asdepicted in FIGS. 3, 3N, 3O, an arrangement of valves allow AHX system700 to be activated or bypassed depending on the mode (e.g., modes 1002,1004, or other modes, transitions, or state as further described withrespect to, for example, FIG. 11 ). A set of three valves, 323, 324, 325direct working fluid flow through the AHX system 700 during generationmode, as illustrated in FIG. 3O, and direct working fluid to bypass theAHX system 700 during charge mode, as illustrated in FIG. 3N. To directworking fluid flow through the AHX system 700 during generation mode,valve 323 may be closed and valves 324 and 325 open. Conversely, tobypass AHX system 700, valve 323 may be opened and valves 324 and 325may be closed. FIGS. 3I and 3J and their corresponding disclosurefurther illustrate the bypass and active states of AHX system 700.Alternatively, in another embodiment, valve 325 may be omitted andvalves 323 and 324 are used to provide a mode-switchable heatdissipation system, as further illustrated and described herein and withrespect to FIGS. 3K and 3L.

Inventory Control System

Inventory control refers to control of the mass, and correspondingpressures, of working fluid in the high-pressure and low-pressure sidesof working fluid loop 300, which can be controlled to affect, forexample, power generation and charge characteristics of the PHES system1000. Control of working fluid inventory inside working fluid loop 300can be accomplished with components illustrated in FIG. 3 , andadditionally illustrated as ICS 300B in FIG. 3M. One or morecontrollers, such as illustrated in FIG. 24 , may participate in and/ordirect the control. Using inventory control, power of the PHES system1000 is preferably modulated by adjusting working fluid pressure in thelow-pressure side of the working fluid loop 300.

In one example of inventory control, a high-pressure tank system and alow-pressure tank system and associated valves are used to control theamount of working fluid circulating in the working fluid loop 300.High-pressure tank system 320, which may include one or more fluid tanksfor holding working fluid, can be connected to a high-pressure workingfluid path via valve 321 and to a low-pressure working fluid path viavalve 322. Low-pressure tank system 310, which may include one or morefluid tanks, can be connected to a high-pressure working fluid path viavalve 311 and to a low-pressure working fluid path via valve 312. Thefour valves, 311, 312, 321, and 322, may be used to control thedirection of working fluid flow between the tank systems 310, 320 andlow-pressure or high-pressure fluid paths in the working fluid loop 300,effectively allowing the addition or removal of working fluidcirculating through the working fluid loop 300.

ICS 300B further includes a make-up working fluid compressor 303 thatcan add working fluid to the system. The working fluid loop 300 operatesas a closed loop; however, working fluid may be lost over time orintentionally lost due to operational decisions or hardwareprotection-related operations, such as venting of working fluid inoverpressure conditions. Working fluid can be added to the working fluidloop 300 by adding outside working fluid through a working fluid filter301. To get the outside working fluid into the high-pressure tank system320, the working fluid compressor 303 is used to pressurize outsideworking fluid to a pressure greater than the high-pressure tank system320 (or greater than at least one tank in the high-pressure tank system320). In an embodiment where the working fluid is air, ambient air maybe brought in through the filter 301 and pressurized with the compressor303. In other embodiments, an outside working fluid make-up reservoir(not shown) may supply working fluid to the filter 301 or the compressor303.

In another example of inventory control, after a normal shutdown or atrip event in PHES system 1000, pressure in working fluid loop 300 ispreferably brought to a lower pressure before either CPT powertrain 100or GPT powertrain 200 is started. This is beneficial because if highpressure in high-pressure fluid paths of the working fluid loop 300 isnot lowered prior to certain mode transitions, the resulting settle-outpressure throughout the working fluid loop 300 would require thatlow-pressure fluid paths in the working fluid loop 300 be designed towork with a higher pressures than typical operating pressures in thelow-pressure fluid paths during charge or generation modes. Thus, ifworking fluid can be removed from the working fluid loop 300 duringspin-down (e.g., transition to hot turning mode 1006 and/or slow rollingstate), lower-pressure piping and components can be used in thelow-pressure fluid paths of the working fluid loop 300, thus allowingreduced capital investment in the PHES system design. Therefore, it isdesirable to bring the circulating working fluid mass down so that thesettle-out pressure in the working fluid loop 300 is no more than thetypical low-side pressure in the working fluid loop 300.

In one example, working fluid loop 300 pressure reduction can beaccomplished by using the working fluid compressor 303 to take workingfluid from a high-pressure fluid path via valve 305, or working fluidfrom a low-pressure fluid path via valve 304, preferably one at a time,and push the working fluid into the high-pressure tank system 320.Additionally or alternatively, valves 311 or 318 can be used to slowlyor quickly bleed down pressure from a high-pressure fluid path into thelower pressure tank system 310.

In another example, ICS 300B includes at least one evacuation valve 308controllable to vent working fluid from the low-pressure side of workingfluid loop 300, as well as pressure relief devices throughout theworking fluid loop 300 to provide protection from overpressure.

In another example, ICS 300B includes at least one evacuation valve 314controllable to vent working fluid from the high-pressure side ofworking fluid loop 300, as well as pressure relief devices throughoutthe working fluid loop 300 to provide protection from overpressure.

Powertrain Bypass/Recirculation Loops

For each turbomachinery powertrain (e.g., CPT powertrain 100 and GPTpowertrain 200), there are working fluid recirculation and bypass loops.A recirculation loop may be characterized as a switchable closed-loopworking fluid path that allows recirculation of working fluid from theoutlet of a component back to the inlet of the component. For example, arecirculation loop can be used around a compressor system during hotturning. In this example, working fluid is routed from the compressorsystem outlet back to the compressor inlet instead of through the mainheat exchangers, allowing the compressor system to gradually cool downafter the compressor system transitions from high flow rate operation(e.g. charge mode 1002 or generation mode 1004) to low flow rateoperation (e.g., hot turning mode 1006).

A bypass loop may be characterized as a switchable closed-loop workingfluid path that routes working fluid around one or more components inthe main working fluid loop 300. For example, during transition from ageneration mode 1004 to a trip mode 1012, a bypass loop may be activatedduring that high flow rate period. The bypass loop could route high flowrate working fluid from a generation compressor system outlet away fromthe heat exchangers and to a generation turbine system inlet. A bypassloop can be beneficial during trip events (e.g., mode 1012) when surgingof the turbomachinery is a risk, and also during turbomachinery startupwhen it is desirable to reduce startup power.

For the CPT system 100, valve 119, which is normally closed, can open apreferably high flow rate bypass loop around the charge compressorsystem 130. This is beneficial, for example, to prevent surge in thecharge compressor system 130 during a trip event from charge mode.

For the CPT system 100, valve 132, which is normally closed, can open arecirculation loop around the charge compressor system 130. The valve132 recirculation loop can be activated to allow circulation and alsocooling of the working fluid through the heat exchanger 132. The valve132 recirculation loop may have lower flow rate capability than thevalve 119 recirculation loop. The valve 132 recirculation loop can bebeneficial, for example, during a hot turning mode for the CPT system100.

For the CPT system 100, valve 142, which is normally closed, can open arecirculation loop around the charge turbine system 140 to allowrecirculation during, for example, hot turning mode for the CPT system100. As previously noted, fan 142F may assist with working fluid flow inthis recirculation loop.

For the GPT system 200, valve 229, which is normally closed, can open apreferably high flow rate bypass fluid path from the outlet of thegeneration compressor system 230 to the outlet fluid path of thegeneration turbine system 240 to reduce start-up power at GPT system200. Routing working fluid through the valve 229 bypass loop reduces themagnitude of power for each of the compressor system 230 and the turbinesystem 240, and thus reduces the net power magnitude of the GPT system200. In effect, the valve 229 bypass loop creates a limited starvingeffect in the GPT system 200. The effect on the turbine system 240 isgreater than the effect on the compressor system 230. Consequently,opening the valve 229 bypass loop can keep turbine system 240 powerproduction less than compressor system 230 power draw. Because thatensures a net electrical power input need, generator system 110 muststill act as a motor during the duration of spin-up. Beneficially, thismaintains VFD control of the spin-up process. As another benefit,opening the valve 229 bypass loop can provide surge protection during atrip event.

For the GPT system 200, valve 232, which is normally closed, can open arecirculation loop around the generation compressor system 230 toprovide working fluid circulation through the generation compressorsystem 230 during, for example, hot turning mode 1006 for the GPT system200.

For the GPT system 200, valve 242, which is normally closed, can open arecirculation loop around the generation turbine system 240. Thisrecirculation loop can be activated to allow circulation and alsocooling of the working fluid recirculating through the heat exchanger242H, thereby cooling the generation turbine system 240. This isbeneficial during, for example, hot turning mode 1006 for the GPT system200.

For the GPT system 200, valve 222, which is normally closed, can beopened to provide to provide a working fluid bypass path around thehigh-pressure side of RHX system 400 and HHX system 500. This is furtherdescribed above with respect to valve 222 and valve 401.

Other recirculation and bypass valves may be implemented in a PHESsystem, such as PHES system 1000, to provide functionality in surgeprevention, overspeed prevention, overpressure prevention, startup loadreduction, and low thermal ramping of components.

F. Hot-Side Thermal Storage Subsystem

FIG. 4 is a schematic fluid path diagram of a hot-side thermal storagesystem which may be implemented in a PHES system, such as PHES system1000, according to an example embodiment. Other embodiments of an HTSsystem operable in PHES systems disclosed herein are possible as well.FIG. 4 provides additional detail concerning an HTS system 501embodiment than is shown in the top-level schematic of FIG. 2 . Ingeneral terms, HTS system 501 includes tanks for HTS medium, HTS mediumfluid paths, pumps, valves, and heaters. The HTS system 501 is capableof transporting HTS medium 590 back and forth between the two (or more)storage tanks to allow charging of the warm HTS medium 590 (i.e., addingthermal energy) or discharging of the HTS medium 590 (i.e., extractingthermal energy). The heaters are available to ensure that the HTS medium590 remains in liquid phase for anticipated operational conditions inPHES system 1000.

An HTS system, such as the embodiment of HTS system 501 illustrated inFIG. 4 , can serve numerous roles within a PHES system, such as PHESsystem 1000. An HTS system may ensure that HTS medium 590 remains inliquid phase during all modes of operation of the PHES system 1000. AnHTS system may deliver HTS medium 590 flow to the HHX system 500 tostore heat in the HTS medium 590 during charge mode operation of thePHES system 1000 (e.g. mode 1002). An HTS system may deliver HTS medium590 flow to the HHX system 500 to provide heat from the HTS medium 590to the working fluid during generation mode operation of the PHES system1000 (e.g., mode 1004). An HTS system may drain HTS medium 590 from thePHES system 1000 into at least one storage tank. An HTS system may vententrapped gas in HTS medium 590 fluid paths. An HTS system may protectfluid paths and components from over pressurization. An HTS system mayisolate itself from the other PHES 1000 subsystems when the HHX system500 is disconnected for service, or for thermal rebalancing of the HTSsystem and/or PHES system 1000. An HTS system may maintain pressure ofthe HTS medium 590 in the HHX system 500 to be less than that of theworking fluid pressure in the working fluid loop 300 at HHX system 500,for example, to prevent leakage of HTS medium into the working fluidloop 300.

In the embodiment of an HTS system shown in FIG. 4 , the HTS system 501includes two tanks: a warm HTS tank 510 for storing warm HTS medium 590(e.g., at approximately 270° C.) and a hot HTS tank 520 for storing hotHTS medium 590 (e.g., at approximately 560° C.). In other embodiments,more than one tank may be used to increase the storage capacity of thewarm HTS storage 591 and/or the hot HTS storage 592. Each HTS tank 510,520 has a pump, an immersion heater, and sensors.

In HTS system 501, warm HTS pump 530 circulates HTS medium 590 from warmHTS tank 510, through fluid interconnect 8, through HHX system 500,through fluid interconnect 6, and to the hot HTS tank 520 during PHEScharging mode 1002, where the HTS medium 590 is absorbing heat from theworking fluid side of the HHX system 500. Hot HTS pump 540 circulatesHTS medium 590 from hot HTS tank 520, through fluid interconnect 6,through HHX system 500, through fluid interconnect 8, and to the warmHTS tank 510 during PHES system generation mode 1004, where the HTSmedium 590 is providing heat to the working fluid side of the HHX system500.

In HTS system 501, valves in HTS system 501 can be actuated to bypassthe HHX system 500 as necessary in order to isolate HTS tanks 510, 520from the rest of PHES system 1000 and/or to facilitate thermal balancingof the HTS loop and/or PHES system. The ability to facilitate balancingcan be beneficial, for example, to maintain thermal balance between PHESsystem charge and generation cycles. It is desirable that the mass ofHTS medium 590 transferred from warm HTS tank 510 to hot HTS tank 520during charge (e.g. charge mode 1002) is later transferred back from hotHTS tank 520 to warm HTS tank 510 during generation (e.g., generationmode 1004), and vice versa. However, disturbances to the HTS medium flowrate during charge and generation cycles, resulting from, for example,uneven heat loss across the PHES system 1000, may result in unequalmasses of HTS medium 590 transferred between the cycles. If that occurs,direct transfer of HTS medium 590 from warm HTS tank 510 to hot HTS tank520, or vice versa, may be used to re-balance HTS medium 590 masses atthe beginning or end of a charge or generation cycle.

In HTS system 501, valves can be actuated to drain HTS medium 590 influid paths, including HHX system 500, into one or more tanks asnecessary.

In HTS system 501, heat traces can be used throughout the fluid paths toavoid formation of solid HTS medium 590 during filling of the HTS system501 and/or during hot turning mode 1006 or hot standby mode 1008 wherethere may be no significant flow of HTS medium 590 through fluid paths.

The following paragraphs describe components of the HTS system 501:

Warm HTS tank 510 is a tank for storing warm HTS medium 590. In otherembodiments, there may be additional warm HTS tanks.

Sensors 510S, 520S are monitoring and reporting devices that can providetemperature and/or fluid level data for HTS medium 590 in tanks 510,520, respectively, to one or more control systems controlling and/ormonitoring conditions in the PHES system 1000.

Valve 511 is a bypass valve that provides a flow path for HTS medium 590to go directly into the warm tank 510, bypassing the pump 530 when valve557 is closed.

Heater 512 provides heat to HTS medium 590 in warm HTS tank 510, forexample, to ensure it stays in liquid form.

Hot HTS tank 520 is a tank for storing hot HTS medium 590. In otherembodiments, there may be additional hot HTS tanks.

Valve 521 is a bypass valve that provides a flow path for HTS medium 590to go directly into the hot tank 520, bypassing the pump 540 when valve558 is closed.

Heater 522 provides heat HTS medium 590 in hot tank 520, for example, toensure it stays in liquid form.

Breather device 529 allows ambient air in and out of the tank head spaceas the HTS medium 590 expands and contracts with temperature.

Warm HTS pump 530 delivers HTS medium 590 from warm HTS tank 510 to hotHTS tank 520 via HHX system 500 during charge mode operation. Dependingon valve state, pump 530 can alternatively or additionally deliver HTSmedium 590 to hot HTS tank 520 via bypass valve 551, bypassing HHXsystem 500, for balancing purposes. In other embodiments, there may beadditional warm HTS pumps.

Hot HTS pump 540 delivers HTS medium 590 from hot HTS tank 520 to warmHTS tank 510 via HHX system 500 during generation mode operation.Depending on valve state, pump 540 can alternatively or additionallydeliver HTS medium 590 to warm HTS tank 510 via valve 551, bypassing HHXsystem 500, for balancing purposes. In other embodiments, there may beadditional hot HTS pumps.

Valve 551 is an HHX system 500 bypass valve that provides a fluid flowpath allowing HTS medium 590 to travel between HTS tanks 510, 520 whilebypassing HHX system 500.

Sensors 5515, 552S are monitoring and reporting devices that can providetemperature, flow, and/or pressure data to one or more control systemscontrolling and/or monitoring conditions in the PHES system 1000.

Valve 552 is a drain valve that provides a fluid flow path for drainingof HTS medium 590 into or out of warm tank 510.

Valve 553 is a drain valve that provides a fluid flow path for drainingof HTS medium 590 into or out of hot tank 520.

Valve 554 is a check valve that works as a gas release valve to allowaccumulated gas in the HTS system 501 to migrate to a tank cover gasspace in either or both tanks 510, 520.

Valve 555 is an HHX system 500 isolation valve that restricts HTS medium590 flow between the HHX system 500 and HTS system 501 throughinterconnect 8.

Valve 556 is an HHX system 500 isolation valve that restricts HTS medium590 flow between the HHX system 500 and HTS system 501 throughinterconnect 6.

Valves 552, 553, 555, and 556 can all be closed to isolate HHX system500 from HTS medium 590 in the HTS system 501.

Valve 557 is a warm CTS pump 530 outlet valve that can be opened toallow CTS medium 590 flow from warm CTS pump 530 or closed to preventflow into the outlet of hot CTS pump 530.

Valve 558 is a hot CTS pump 540 outlet valve that can be opened to allowCTS medium 590 flow from hot CTS pump 540 or closed to prevent flow intothe outlet of hot CTS pump 540.

Heat trace 560 can be activated to maintain fluid paths and/or othermetal mass at temperatures sufficient to keep the HTS medium 590 inliquid phase, and/or at desired setpoint temperatures during variousmodes and/or states of PHES system 1000 in order to reduce thermalgradients on sensitive components, and/or to reduce transition timebetween PHES system 1000 modes and states. Beneficially, heat trace 560can reduce thermal ramp rates, which benefits component longevity, andallows for faster startup times. Heat trace 560 is illustrated as nearfluid interconnect 8 and on the warm tank 510 side of HTS system 501.However, heat trace 560 can be located at other locations within HTSsystem 501 in order to accomplish its functions. Additionally oralternatively, heat trace 560 can include heat traces at multiplelocations within HTS system 501 in order to accomplish its functions.

Operation of HTS System

During PHES system 1000 generation mode 1004, the HTS system 501 isconfigured such that hot HTS medium 590 is delivered from hot HTS tank520 to warm HTS tank 510 via HHX system 500 at a fixed and/orcontrollable rate using pump 540. During generation, heat from the hotHTS medium 590 is transferred to the working fluid via the HHX system500. The rated generation flow of HTS medium 590 at a given PHES system1000 power may be a function of the generation flow of CTS medium 690 tomaintain inventory balance.

During PHES system 1000 charge mode 1002, the HTS system 501 isconfigured such that warm HTS medium 590 can be delivered from warm HTStank 510 to hot HTS tank 520 via HHX system 500 at a fixed orcontrollable rate using the pump 530. During charge, the warm HTS medium590 absorbs heat from the hot working fluid via the HHX system 500. Therated charge flow of HTS medium 590 at a given PHES system 1000 powermay be a function of the charge flow of CTS medium 690 to maintaininventory balance.

Under some PHES system 1000 modes, such as long-term Cold Dry Standby,the HTS medium 590 in the hot-side loop (e.g., HTS system 501, HHXsystem 500, and intermediate fluid paths) needs to be drained to the HTStanks 510 and/or 520. In this scenario, preferably the heater 512 in thewarm tank 510 is used to ensure HTS medium 590 remain in liquid form.Preferably, for example, the hot HTS pump 540 can be used to transferhot HTS medium 590 from the hot HTS tank 520 to the warm HTS tank 510via the HHX system 500 bypass line (e.g., via valve 551) and valve 511.Alternatively, warm HTS pump 530 can be used to transfer warm HTS medium590 from the warm HTS tank 510 to the hot HTS tank 520 via the HHXsystem 500 bypass line (e.g., via valve 551) and valve 521. HTS 590medium remaining in hot HTS tank 520 may also be kept in a liquid statewith heater 522.

Under certain operating modes, HHX system 500 can be bypassed by closingvalves 552, 553, 555, and 556, opening valve 551, and using pump 530 or540 to cause flow of HTS medium 590 between HTS tanks 510 and 520 Forexample, HHX system 500 can be bypassed to balance the thermal energycontent either between the HTS tanks 510, 520 individually and/or tobalance total thermal energy between HTS system 501 and CTS system 601.

G. Cold-Side Thermal Storage Subsystem

FIG. 5 is a schematic fluid path diagram of a cold-side thermal storagesystem which may be implemented in a PHES system, such as PHES system1000, according to an example embodiment. Other embodiments of an CTSsystem operable in PHES systems disclosed herein are possible as well.FIG. 5 provides additional detail concerning a CTS system 601 embodimentthan is shown in the top-level schematic of FIG. 2 . In general terms,CTS system 601 includes tanks for CTS medium, CTS medium fluid paths,pumps, valves, and inert gas supply. The CTS system 601 is capable oftransporting CTS medium 690 back and forth between the two (or more)storage tanks to allow charging of the CTS medium 690 (i.e., removingthermal energy) or discharging of the CTS medium 690 (i.e., addingthermal energy). During PHES system 1000 charge mode operation, the CTSmedium 690 deposits heat to working fluid inside the CHX system 600.During PHES system 1000 generation mode operation, the CTS medium 690absorbs heat from the working fluid inside the CHX system 600.

A CTS system, such as CTS system 601 illustrated in FIG. 5 , can servenumerous roles within a PHES system, such as PHES system 1000. A CTSsystem may deliver CTS medium 690 flow to the CHX system 600 to provideheat during charge mode operation of PHES system 1000 (e.g., mode 1002).A CTS system may deliver CTS medium 690 flow to the CHX system 600 toabsorb heat during generation mode operation of the PHES system 1000(e.g., mode 1004). A CTS system may drain CTS medium 690 into at leastone storage tank. A CTS system may vent entrapped gas in CTS medium 690fluid paths. A CTS system may protect fluid paths and components fromover pressurization. A CTS system 601 may isolate itself from other PHES1000 subsystems when the CHX system 600 is disconnected for service, orfor thermal rebalancing. A CTS system may isolate the CTS medium 690from ambient via an inert gas blanket. A CTS system may maintainpressure of the CTS medium 690 in the CHX system 600 to be less thanthat of the working fluid pressure in the working fluid loop 300 at CHXsystem 600, for example, to prevent leakage of CTS medium into theworking fluid loop 300. A CTS system 601 may monitor CTS medium 690health during operation.

In the embodiment of a CTS system shown in FIG. 5 , the CTS system 601includes two tanks: a warm CTS tank 610 for storing warm CTS medium 690(e.g., at approximately 30° C.) and a cold CTS tank 620 for storing coldCTS medium 690 (e.g., at approximately −60° C.). In other embodiments,more than one CTS tank may be used to increase the storage capacity ofthe warm CTS storage 691 and/or the cold CTS storage 692. In CTS system601, each CTS storage 691, 692 has a pump system 639, 649, respectively.

In CTS system 601, warm pump 630 circulates CTS medium 690 from warm CTStank 610, through fluid interconnect 1, through CHX system 600, throughfluid interconnect 13, and to the cold CTS tank 620 during PHES 1000charging mode 1002, where the CTS medium 690 is providing heat to theworking fluid side of the CHX system 600. The cold pump 640 circulatesCTS medium 690 from cold CTS tank 620, through fluid interconnect 13,through CHX system 600, through fluid interconnect 1, and to the warmCTS tank 610 during PHES system 1000 generation mode 1004, where the CTSmedium 690 is absorbing heat from the working fluid side of the CHXsystem 600.

Valves in CTS system 601 can be actuated to bypass the CHX system 600 asnecessary in order to isolate CTS storage 691, 692 from the rest of PHESsystem 1000 and/or to facilitate balancing of the CTS loop. The abilityto facilitate balancing can be beneficial, for example, to maintainthermal balance between PHES system charge and generation cycles. It isdesirable that the mass of CTS medium 690 transferred from warm CTS tank610 to cold CTS tank 620 during charge (e.g. charge mode 1002) is latertransferred back from cold CTS tank 620 to warm CTS tank 610 duringgeneration (e.g., generation mode 1004). However, disturbances to theCTS flow rate during charge and generation cycles, resulting from, forexample uneven heat loss across the PHES system 1000, may result inunequal masses of CTS medium 690 transferred between the cycles. If thatoccurs, direct transfer of CTS medium 690 from warm CTS tank 610 to coldCTS tank 620, or vice versa, may be used to re-balance CTS medium 690masses at the beginning or end of a charge or generation cycle.

In CTS system 601, valves can be actuated to drain CTS medium 690 influid paths, including CHX system 600, into one or more tanks asnecessary.

In an embodiment of CTS system 601, one, or both of, CTS pumps 630, 640are capable of bidirectional flow. Beneficially, reverse pumping can beused to provide active pressure reduction in the CTS loop, which can beemployed to keep CTS medium 690 pressure in CHX system 600 below workingfluid pressure in CHX system 600. This working fluid positive pressurecondition (with respect to CTS medium 690) beneficially prevents any CTSmedium from leaking into the working fluid loop 300 (e.g., throughcracked heat exchanger cores).

The following paragraphs describe components of the CTS system 601:

Valve 602 is a CHX system 600 isolation valve that restricts CTS medium690 flow between the CHX system 600 and CTS system 601 throughinterconnect 13.

Valve 603 is a CHX system 600 isolation valve that restricts CTS medium690 flow between the CHX system 600 and CTS system 601 throughinterconnect 1.

Valves 602, 603 can both be closed to isolate the CHX system 600 fromCTS medium 690 in the CTS system 601.

Valve 605 is a CHX system 600 bypass valve that provides a fluid flowpath allowing CTS medium 690 to travel between CTS tanks 610, 620 whilebypassing CHX system 600.

Warm CTS tank 610 is a tank for storing warm CTS medium 690.

Sensors 610S, 620S are monitoring and reporting devices that can providetemperature and/or fluid level data for HTS medium 690 in tanks 610,620, respectively, to one or more control systems controlling and/ormonitoring conditions in the PHES system 1000.

Valve 611 is an isolation valve that isolates warm CTS tank 610 from theCTS loop.

Pressure relief device 619 protects CTS tanks 610, 620 from overpressurization via a gas fluid path between the headspace of CTS tanks610, 620.

Cold CTS tank 620 is a tank for storing cold CTS medium 690.

Valve 621 is an isolation valve that isolates cold CTS tank 620 from theCTS loop.

Inert gas reservoir 622 is a storage reservoir for an inert gas (e.g.,nitrogen) useable as a cover gas to blanket CTS medium 690 in tanks 610,620.

Valve 623 is an inert gas fluid path valve that can control a flow ofinert gas from inert gas reservoir 622 to the headspace of CTS tanks620, 621 which are connected via a gas fluid path. Valve 623 can be usedto regulate the pressure of an inert gas blanket within the CTS tanks610, 620.

Valve 624 is an inert gas purge valve that can control a flow ofpressurized inert gas into the cold-side loop CTS medium 690 fluid pathsto purge those fluid paths of CTS medium 690.

Warm CTS pump 630 delivers CTS medium 690 from warm CTS tank 610 to coldCTS tank 620 via CHX system 600 during charge mode operation of the PHESsystem 1000 (e.g., mode 1002). Depending on valve states, pump 630 canalternatively or additionally deliver CTS medium 690 to cold CTS tank620 via valve 605, bypassing CHX system 600, for balancing purposes. Inother embodiments, there may be additional warm CTS pumps.

Valve 631 is a warm pump 630 isolation valve that, when closed, canisolate pump 630, for example during PHES system 1000 generation modewhen CTS medium 690 is flowing from cold CTS tank 620 to warm CTS tank610. In an embodiment where pump 630 is bidirectional and operating inreverse, valve 631 may be open during generation mode to allow activepressure reduction in the CTS loop.

Valve 632 is a warm CTS pump 630 bypass valve that provides a flow patharound pump 630 during, for example, generation mode operation of thePHES system 1000 (e.g., mode 1004) or balancing of CTS medium 690 in CTSsystem 601.

Valve 633 is a warm pump 630 isolation valve that, when closed alongwith warm pump outlet valve 631, allows for servicing of warm pump 630when the pump is not in use, for example during PHES system 1000generation mode when CTS medium 690 is flowing to warm tank 610 throughpump 630 bypass valve 632.

Warm CTS pump system 639 and cold CTS pump system 649 illustraterespective CTS medium 690 pumping systems for warm CTS storage 691 andcold CTS storage 692, respectively.

Cold pump 640 delivers CTS medium 690 from cold CTS tank 620 to warm CTStank 610 via CHX system 600 during generation mode operation of the PHESsystem 1000 (e.g., mode 1004). Depending on valve state, pump 640 canalternatively or additionally deliver CTS medium 690 to warm CTS tank620 via valve 605, bypassing CHX system 600, for balancing purposes. Inother embodiments, there may be additional cold CTS pumps.

Valve 641 is a cold pump 640 isolation valve that, when closed, canisolate pump 640, for example during PHES system 1000 charge mode whenCTS medium 690 is flowing from warm CTS tank 610 to cold CTS tank 620.In an embodiment where pump 640 is bidirectional and operating inreverse, valve 641 may be open during generation mode to allow activepressure reduction in the CTS loop.

Valve 642 is a cold CTS pump 640 bypass valve that provides a flow patharound pump 640 during, for example, charge mode operation of the PHESsystem 1000 (e.g., mode 1002) or balancing of CTS medium 690 in CTSsystem 601.

Valve 643 is a cold pump 640 isolation valve that, when closed alongwith cold pump outlet valve 641, allows for servicing of cold pump 640when the pump is not in use, for example during PHES system 1000 chargemode when CTS medium 690 may be flowing to cold tank 620 through pump640 bypass valve 642.

Sensors 661S, 662S, 663S, 664S, 665S, 666S, 667S, 668S are monitoringand reporting devices that can provide temperature, flow, and/orpressure data to one or more control systems controlling and/ormonitoring conditions in the PHES system 1000.

Valve 682 is a check-style vent valve that allows entrapped CTS medium690 gas in CTS loop fluid paths (e.g., CTS system 601 and CHX system600) to be vented to a cover gas region of the CTS tanks 610, 620, butprevents gas or fluid from the CTS tanks from flowing back towards CHXsystem 600.

Operation of CTS System

During PHES system 1000 charge mode 1002, warm pump 630 delivers warmCTS medium 690 at a fixed or controllable rate from warm CTS tank 610 tocold CTS tank 620 via CHX system 600. During charge, heat from the warmCTS medium 690 is transferred to the working fluid via the CHX system600. The rated charge flow of CTS medium 690 at a given PHES system 1000power may be a function of the charge flow of HTS medium 590 to maintaininventory balance. The cold CTS pump 640 can be used to reduce pressureat the CHX system 600 by pulling CTS medium 690 from there.

During PHES system 1000 generation mode 1004, the cold pump 640 deliverscold CTS medium 690 at a fixed or controllable rate from the cold CTStank 620 to the warm CTS tank 610 through CHX system 600. The ratedgeneration flow of CTS medium 690 at a given PHES system 1000 power maybe a function of the generation flow of HTS medium 590 to maintaininventory balance. The warm coolant pump 630 can be used to reducepressure at the CHX system 600 by pulling CTS medium 690 from there.

Under some PHES system 100 modes, such as long-term Cold Dry Standby,the CTS medium 690 in the cold-side loop (e.g., CTS system 601, CHXsystem 600, and intermediate fluid paths) needs to be drained to the CTStanks 610 and/or 620. For example, cold pump 640 can be used to transfercold CTS medium 690 in the cold tank 620 to the warm tank 610 via afluid path through bypass valve 605.

Under certain operating modes, CHX system 600 can be bypassed by closingvalves 602, 603 and opening valve 605, and using pumps 630 and/or 640 tocause flow of CTS medium 690 between CTS tanks 610 and 620. For example,CHX system 600 can be bypassed to balance the thermal energy contenteither between CTS tanks 610, 620 individually and/or to balance totalthermal energy between CTS system 601 and HTS system 501.

III. Operating Modes and States in a PHES System

Disclosed herein are various modes of operation and states of a PHESsystem, each of which may be implemented in the exemplary PHES system1000.

A. Primary Modes of Operation

The PHES systems herein, including PHES system 1000, can transitionthrough a number of modes of operation. Each of the primary modes ofoperation can be described with respect to a particular state ofcomponents and subsystems in the PHES system. Additionally, each of theprimary modes of operation has an associated active parasitic load and areadiness time. Example primary modes of operation of the disclosed PHESsystems are shown in FIG. 10 .

FIG. 10 illustrates primary modes of operation of a PHES system,including PHES system 1000, according to an example embodiment. Theprimary modes of operation include charge 1002, generation 1004, hotturning 1006, hot standby 1008, cold dry standby 1010, and tripped 1012.FIG. 10 further illustrates the preferred transitions between modes, asindicated by directional arrows between modes. For example, in oneembodiment, a PHES system, such as PHES system 1000, can transition fromcharge 1002 to hot turning 1006 to hot standby 1008 to cold dry standby1010. In another example, a PHES system, such as PHES system 1000, cantransition from charge 1002 to hot turning 1006 to generation 1004.

Cold Dry Standby Mode 1010. In this primary mode of operation, thethermal storage reservoirs are effectively offline and the associatedthermal storage media are at their lowest practical thermal energy statefor a given embodiment. In embodiments with liquid thermal storage, thethermal storage media may be drained to their respective tanks and notcirculated through the rest of the PHES system. In embodiments with ahot-side liquid thermal storage media (e.g., molten salt), the hot-sideliquid thermal storage media may be kept at a minimum temperature toprevent freezing, which may include active heating to maintain thisminimum practical thermal energy state. In embodiments with a coolant asa cold-side liquid thermal storage media, the coolant may be kept at ornear environmental ambient temperature. In some embodiments, theremainder of the PHES system infrastructure may also be kept at or nearenvironmental ambient temperature. In some embodiments, pressure in theworking fluid loop may be kept at or near ambient environmental pressureor at a minimum working fluid pressure P_(standby). In one embodiment,P_(standby) is a pressure in the working fluid loop (e.g., working fluidloop 300) below working pressure (e.g., during charge or generationmodes 1002, 1004) but still sufficient to ensure positive pressure withrespect to any opposite side pressure in HTS medium or CTS medium heatexchanger systems (e.g., HHX system 501 or CHX system 601). MaintainingP_(standby) beneficially prevents any HTS medium or CTS medium fromleaking into the working fluid loop (e.g., through cracked heatexchanger cores).

In Cold Dry Standby mode 1010, a PHES system achieves its lowest activeparasitic load. In some embodiments, there is no significant parasiticload. In some embodiments, heating a hot-side liquid thermal storagemedia to prevent freezing is an active parasitic load. In someembodiments, maintaining a working fluid pressure at P_(standby) greaterthan ambient environmental pressure is an active parasitic load.

Within embodiments of the disclosed PHES systems, including PHES system1000, the readiness time to transition between cold dry standby mode1010 and either charge mode 1002 or generation mode 1004 (via hotstandby mode 1008) is a relatively long time compared to other modetransitions to charge mode 1002 or generation mode 1004.

Hot Standby Mode 1008. In this primary mode of operation, heatexchangers are primed with thermal storage media. In some embodiments,hot-side and/or cold-side heat exchangers are filled partially orcompletely with HTS and/or CTS media, respectively. In the case ofliquid thermal storage media, the thermal storage media may or may notbe continuously flowing through the heat exchangers, preferably at avery low flow rate. One or more hot-side heat exchangers (e.g., HHXsystem 500) are warmed above ambient environmental temperature. In someembodiments, heat traces or other heaters (e.g., heaters 512, 522) areused to heat the HTS medium, which in turn warms the hot-side heatexchanger(s). The warmed hot-side heat exchangers may be at or neartheir steady-state temperature for charge or generation modes, or may beat an intermediate temperature between their steady-state temperatureand ambient environmental temperature. CPT system (e.g., CPT system 100)and GPT system (e.g., GPT system 200) are at zero RPM or substantiallyzero RPM (e.g., no turning, temporarily spinning down to eventual zeroRPM from a prior state, insubstantial turning as a result of convectivecurrents only, and/or no torque input from motors). In some embodiments,minimum pressure in the working fluid loop is kept at P_(standby),though pressure in the working fluid loop (e.g. working fluid loop 300)may be higher initially upon entering hot standby mode 1008, dependingon the prior mode the PHES system is transitioning from.

In hot standby mode, embodiments of the disclosed PHES systems canexperience active parasitic load from heaters working on the thermalstorage media. In some embodiments, heat traces are active to keep thethermal storage media at or near steady-state temperatures. In someembodiments, maintaining a working fluid pressure at P_(standby) is anactive parasitic load.

Within embodiments of the disclosed PHES systems, including PHES system1000, and beneficially, the readiness time to transition between hotstandby mode 1008 and either charge mode 1002 or generation mode 1004 isrelatively short. For example, the readiness time may be less than 10%of the readiness time for transition from cold dry standby mode 1010 toeither charge mode 1002 or generation mode 1004.

Hot Turning Mode 1006. In this primary mode of operation, either or boththe CPT system and/or GPT system is slow rolling (i.e., CPT and/or GPTturbomachinery is spinning at a minimum speed). In a preferredembodiment, the slow-rolling turbomachinery use recirculation and/orbypass fluid loops, such as the examples disclosed herein, to circulateworking fluid through the slow-rolling turbomachinery.

Within embodiments of the disclosed PHES systems, including PHES system1000, and beneficially, the readiness time to transition between hotturning mode 1006 and either charge mode 1002 or generation mode 1004 isshorter than the readiness time to transition between hot standby mode1008 and either charge mode 1002 or generation mode 1004.

Charge Mode 1002. In this primary mode of operation, the CPT systemturbomachinery is connected to the electrical grid and preferablyoperating at grid speed, i.e., the CPT system is operating at an RPMthat synchronizes the motor system with the operating frequency of theconnected electrical grid. In some embodiments, the GPT system is atzero RPM or substantially zero RPM (e.g., no turning, temporarilyspinning down to eventual zero RPM from prior state, insubstantialturning as a result of convective currents only, and/or no torque inputfrom motors). In some embodiments, the GPT system is at turning speed.In charge mode, thermal storage media are substantially at steady-statetemperatures and one or more control systems control may modulate powerconsumption of the disclosed PHES systems by, for example, controllingthe pressure of the working fluid. In another embodiment, one or morecontrol systems may control CTS medium and/or HTS medium flow ratesand/or pressures through the main heat exchanger system to modulatepower consumption of the disclosed PHES systems. In another embodiment,one or more control systems control both the pressure of the workingfluid and/or CTS medium and/or HTS medium flow rates and/or pressures tomodulate power consumption of the disclosed PHES systems.

In charge mode, active parasitic loads include support systems for theheat exchanger systems and any associated fluid loops, support systemsfor CPT system, and in some embodiments, support systems for the GPTsystem if the generation powertrain is turning.

Beneficially, embodiments of the disclosed PHES systems can ramp thecharge mode 1002 power consumption very quickly between full power and asignificantly reduced power consumption level (and vice versa).Additionally, within embodiments of the disclosed PHES systems,including PHES system 1000, and beneficially, the readiness time totransition between charge mode 1002 and generation mode 1004 (or viceversa) via hot turning mode 1006 is shorter than the readiness time totransition between hot standby mode 1008 and either charge mode 1002 orgeneration mode 1004.

Generation Mode 1004. In this primary mode of operation, the GPT systemis connected to the electrical grid and preferably operating at gridspeed, i.e., the GPT system is operating at an RPM that synchronizes thegenerator system with the operating frequency of the connectedelectrical grid. In some embodiments, the charge powertrain is at zeroRPM or substantially zero RPM (e.g., no turning, temporarily spinningdown to eventual zero RPM from prior state, insubstantial turning as aresult of convective currents only, and/or no torque input from motors).In some embodiments, the CPT system is at turning speed. In generationmode, thermal storage media are substantially at steady-statetemperatures. In generation mode, thermal storage media aresubstantially at steady-state temperatures and one or more controlsystems control may modulate power generation of the disclosed PHESsystems by, for example, controlling the pressure of the working fluid.In another embodiment, one or more control systems may control CTSmedium and/or HTS medium flow rates and/or pressures through the mainheat exchanger system to modulate power generation of the disclosed PHESsystems. In another embodiment, one or more control systems control boththe pressure of the working fluid and/or CTS medium and/or HTS mediumflow rates and/or pressures to modulate power generation of thedisclosed PHES systems.

In generation mode, active parasitic loads include support systems forthe heat exchanger systems and any associated fluid loops, supportsystems for GPT system, and in some embodiments, support systems for theCPT system if the charge powertrain is turning.

Beneficially, embodiments of the disclosed PHES systems can ramp thegeneration mode 1004 power generation very quickly between low power andfull power (and vice versa).

Tripped Mode 1012. This primary mode of operation is a state of recoveryfrom a trip event. This mode may include spin-down of one or more of thepowertrains (e.g. CPT system 100, GPT system 200) from its priorcontrolled (e.g., hot turning and/or steady-state) speed to a slower orsubstantially zero RPM speed. In some embodiments, this mode may furtherinclude venting working fluid to manage working fluid pressures and/ormaintain working fluid pressures within design and/or safe workinglimits.

In a tripped mode, active parasitic loads will be consistent withwhatever mode preceded the Tripped mode, except where an activeparasitic load also trips to a failsafe condition with a lower (orhigher) load of the active parasitic loads. PHES system readinessexiting from tripped mode 1012 to another mode will vary depending onthe initiating trip event.

B. PHES System Operating States and Transitional States

Operating States

FIG. 11 is a state diagram illustrating operating states of a PHESsystem, including PHES system 1000, according to an example embodiment.FIG. 11 mirrors the primary modes of operation shown in FIG. 10 ,including the preferred transitions between modes, as indicated bydirectional arrows between modes. FIG. 11 further adds additional detailregarding state conditions. Operating states are shown as headings inthe blocks in FIG. 11 . Some of these states represent differentversions of three common modes of operation (i.e., hot turning 1006,charge 1002, and generation 1004) and account for alternateconfigurations in which the non-primary powertrain may be operating in(e.g., slow rolling or not slow rolling). The PHES system operatingstates illustrated in FIG. 11 are “holding states” in which the PHESsystems spend significant time.

CHARGE (GPT BASE) 1014 is a charge mode 1002 operating state where theGPT system (e.g., GPT system 200) is at a base level with low or noactivity. Valves associated with GPT system operation are configured ata base level (e.g., for no rotation of the GPT system). The CPT system(e.g., CPT system 100) is in charge mode with CPT turbomachineryrotating at steady state (i.e., operating) speed. Valves associated withthe CPT system are configured for steady state rotation of CPTturbomachinery, including connection to high-pressure working fluidpaths. The hot-side loop is configured for HTS medium to flow from awarm HTS system (e.g., warm HTS system 591) to a hot HTS system (e.g.,hot HTS system 592) via an HHX system (e.g., HHX system 500). Thecold-side loop is configured for CTS medium to flow from a warm CTSsystem (e.g., warm CTS system 691) to a cold CTS system (e.g., cold CTSsystem 692) via a CHX system (e.g., CHX system 600). Ambient cooling ofworking fluid (e.g. AHX system 700) is bypassed.

GENERATION (CPT BASE) 1016 is a generation mode 1004 operating statewhere the CPT system (e.g., CPT system 100) is at a base level with lowactivity. Valves associated with CPT system operation are configured ata base level (e.g., for no rotation of the CPT system). The GPT system(e.g., GPT system 200) is in generation mode with GPT turbomachineryrotating at steady state (i.e., operating) speed. Valves associated withthe GPT system are configured for steady-state rotation of GPTturbomachinery, including connection to high-pressure working fluidpaths. The hot-side loop is configured for HTS medium to flow from thehot HTS system (e.g., hot HTS system 592) to the warm HTS system (e.g.,warm HTS system 591). The cold-side loop is configured for CTS medium toflow from the cold CTS system (e.g., cold CTS system 692) to the warmCTS system (e.g., warm CTS system 691). Ambient cooling of working fluid(e.g. AHX system 700) is active with working fluid circulating throughthe AHX system 700.

CHARGE (GPT SLOW ROLLING) 1026 is a charge mode 1002 operating statewhere the GPT system (e.g., GPT system 200) is slow rolling (i.e., GPTturbomachinery is spinning at a minimum speed). Valves associated withGPT system operation are configured for recirculation of working fluidthrough the GPT system. The CPT system (e.g., CPT system 100) is incharge mode with CPT turbomachinery rotating at operating speed. Valvesassociated with the CPT system are configured for steady-state rotationof CPT turbomachinery, including connection to high-pressure workingfluid paths. The hot-side loop is configured for HTS medium to flow fromthe warm HTS system (e.g., warm HTS system 591) to the hot HTS system(e.g., hot HTS system 592). The cold-side loop is configured for CTSmedium to flow from the warm CTS system (e.g., warm CTS system 691) tothe cold CTS system (e.g., cold CTS system 692). Ambient cooling ofworking fluid (e.g. AHX system 700) is bypassed.

GENERATION (CPT SLOW ROLLING) 1028 is a generation mode 1004 operatingstate where the CPT system (e.g., CPT system 100) is slow rolling (i.e.,CPT turbomachinery is spinning at a minimum speed). Valves associatedwith CPT system operation are configured for recirculation of workingfluid through the CPT system. The GPT system (e.g., GPT system 200) isin generation mode with GPT turbomachinery rotating at operating speed.Valves associated with the GPT system are configured for steady-staterotation of GPT turbomachinery, including connection to high-pressureworking fluid paths. The hot-side loop is configured for HTS medium toflow from the hot HTS system (e.g., hot HTS system 592) to the warm HTSsystem (e.g., warm HTS system 591). The cold-side loop is configured forCTS medium to flow from the cold CTS system (e.g., cold CTS system 692)to the warm CTS system (e.g., warm CTS system 691). Ambient cooling ofworking fluid (e.g. AHX system 700) is active with working fluidcirculating through the AHX system 700.

HOT TURNING (CPT SLOW ROLLING) 1018 is a hot turning mode 1008 operatingstate where CPT system (e.g., CPT system 100) is slow rolling (i.e., CPTturbomachinery is spinning at a minimum speed). Valves associated withCPT system operation are configured for recirculation of working fluidthrough the CPT system. GPT system (e.g., GPT system 200) is at a baselevel with low activity. Valves associated with GPT system operation areconfigured at a base level (e.g., for no rotation of the GPT system).Hot-side and cold-side loops are in standby, where the HTS and CTS mediaare resident in the associated heat exchangers and thermal media loopfluid paths (e.g., HHX system 500 and CHX system 600, respectively).Heat traces on the hot-side loop are turned on as necessary to keep HTSmedium in liquid phase. The ambient heat exchanger system (e.g. AHXsystem 700) is set to active state. AHX valves are set to allow workingfluid circulation through the AHX system, but no working fluid mayactually be circulating through the AHX system due to recirculationand/or base state of the working fluid at the powertrain. With noworking fluid circulation through the AHX system, AHX system fans areturned off.

HOT TURNING (GPT SLOW ROLLING) 1022 is a hot turning mode 1008 operatingstate where GPT system (e.g., GPT system 200) is slow rolling (i.e., GPTturbomachinery is spinning at a minimum speed). Valves associated withGPT system operation are configured for recirculation of working fluidthrough the GPT system. CPT system (e.g., CPT system 100) is at a baselevel with low activity. Valves associated with CPT system operation areconfigured at a base level (e.g., for no rotation of the CPT system).Hot-side and cold-side loops are in standby, where the HTS and CTS mediaare resident in the associated heat exchangers and thermal media loopfluid paths (e.g., HHX system 500 and CHX system 600, respectively).Heat traces on the hot-side loop are turned on as necessary to keep HTSmedium in liquid phase. The ambient heat exchanger system (e.g. AHXsystem 700) is set to active state. AHX valves are set to allow workingfluid circulation through the AHX system, but no working fluid mayactually be circulating through the AHX system due to recirculationand/or base state of the working fluid at the powertrain. With noworking fluid circulation through the AHX system, AHX system fans areturned off.

HOT TURNING (CPT+GPT SLOW ROLLING) 1020 is a hot turning mode 1008operating state where GPT system (e.g., GPT system 200) is slow rolling(i.e., GPT turbomachinery is spinning at a minimum speed) and CPT system(e.g., CPT system 100) is slow rolling (i.e., CPT turbomachinery isspinning at a minimum speed). Valves associated with GPT systemoperation are configured for recirculation of working fluid through theGPT system. Valves associated with CPT system operation are configuredfor recirculation of working fluid through the CPT system. Hot-side andcold-side loops are in standby, where the HTS and CTS media are residentin the associated heat exchangers and thermal media loop fluid paths(e.g., HHX system 500 and CHX system 600, respectively). Heat traces onthe hot-side loop are turned on as necessary to keep HTS medium inliquid phase. The ambient heat exchanger system (e.g. AHX system 700) isset to active state. AHX valves are set to allow working fluidcirculation through the AHX system, but no working fluid may actually becirculating through the AHX system due to recirculation and/or basestate of the working fluid at the powertrain. With no working fluidcirculation through the AHX system, AHX system fans are turned off.

HOT STANDBY 1024 is a hot standby mode 1008 operating state. GPT system(e.g., GPT system 200) is at a base level with low activity. Valvesassociated with GPT system operation are configured at a base level(e.g., for no rotation of the GPT system). CPT system (e.g., CPT system100) is at a base level with low activity. Valves associated with CPTsystem operation are configured at a base level (e.g., for no rotationof the CPT system). Hot-side and cold-side loops are in standby, wherethe HTS and CTS media are resident in the associated heat exchangers andthermal media loop fluid paths (e.g., HHX system 500 and CHX system 600,respectively). Heat traces on the hot-side loop are turned on asnecessary to keep HTS medium in liquid phase. The ambient heat exchangersystem (e.g. AHX system 700) is set to active state. AHX valves are setto allow working fluid circulation through the AHX system, but noworking fluid may actually be circulating through the AHX system due tobase state of the working fluid at the powertrain. With no working fluidcirculation through the AHX system, AHX system fans are turned off.

COLD DRY STANDBY 1030 is a cold dry standby mode 1010 operating state.GPT system (e.g., GPT system 200) is off with no significant activity.Valves associated with GPT system operation are configured at a baselevel (e.g., for no rotation of the GPT system). CPT system (e.g., CPTsystem 100) is off with no significant activity. Valves associated withCPT system operation are configured at a base level (e.g., for norotation of the CPT system). HTS and CTS media in hot-side and cold-sideloops, respectively, are drained to HTS and CTS tanks, respectively(e.g., tank(s) 510 and/or 520; tank(s) 610 and/or 620). In oneembodiment, HTS medium 590 in HHX 500 and associated fluid paths isdrained to hot HTS tank 520, and HTS medium 590 in warm HTS tank 510remains in warm HTS tank 510. In another embodiment, CTS medium 690 inCHX 600 and associated fluid paths is drained to warm CTS tank 610, andCTS medium 690 in cold CTS tank 620 remains in cold CTS tank 620.Additionally or alternatively, HTS medium 590 and CTS medium 690 may bepumped between their respective tanks in the same manner as a thermalmedia rebalancing operation. Hot-side and cold-side heat exchangers andassociated thermal media loop fluid paths (e.g., HHX system 500 and CHXsystem 600, respectively) are empty of thermal storage media and HTS andCTS media are not actively circulating. One or more HTS system 501heaters (e.g., heaters 512, 522) are active to maintain HTS mediumresident in tanks (e.g., HTS tanks 510, 520) in liquid state.

Transitional States

In addition to the operating states (i.e., long-term holding states)shown in FIG. 11 , there are numerous additional transitionary states.These transitionary states would be within the paths shown by the arrowsin FIG. 11 . Between operating states, there may be transitional stateswhere one or more subsystems need to switch to their own respectivestates. The subsystems may change their state (e.g., valve actuation,pump speed change) in specific preferred sequences. These transitionsand the intermediary transitionary states that make up the transitionsare described in more detail below.

C. States of Generation Powertrain and Associated Valves

FIG. 12 and FIG. 13 are state diagrams illustrating select operating andtransitional states of a PHES system, including PHES system 1000, eachaccording to an example embodiment. These are example state transitionsand other embodiments are possible as well. FIG. 12 and FIG. 13 are usedprimarily to illustrate generation powertrain state transitions. Otherexamples are provided herein reflecting other state transitions forother subsystems in a PHES system, for example, FIGS. 19, 20, 21, 22,and 23 and their associated descriptions.

FIG. 12 illustrates transition from the HOT STANDBY state 1024 toGENERATION (CPT BASE) state 1016, with intermediate transitional states1034, 1036, 1038. During the transition from the HOT STANDBY state 1024to GENERATION (CPT BASE) state 1016, the generation powertrain movesfrom the base state, at 1024 and 1034, to spin up to variable frequencydrive state, at 1036, to power generation, at 1038 and 1016. The GPTvalve system moves from its base state, at 1024, to bypassed state, at1034 and 1036 and 1038, and then eventually to the connected state, at1016. Beneficially, this overall transition process enables thegeneration powertrain to move through the spin up state with minimalload.

FIG. 13 illustrates transition from the GENERATION (CPT BASE) state 1016to the HOT TURNING (GPT SLOW ROLLING) state 1022, with intermediatetransitional states 1042 and 1044. During the transition from theGENERATION (CPT BASE) state 1016 to the HOT TURNING (GPT SLOW ROLLING)state 1022 (e.g., due to operator initiated shutdown of the generationmode 1004), the generation powertrain moves through the generationstate, at 1016 and 1042, to the base state, at 1044, and then to theturning state, at 1022. The GPT valve systems move from a connectedstate, at 1016, to a bypass state, at 1042 and 1044, beneficially toallow the turbomachinery speed to drop, and eventually to arecirculation state, at 1022, beneficially to allow the rotor to cooldown.

FIG. 14 further describes the generation powertrain (e.g., GPT system200) states (i.e., GPT states) illustrated in FIGS. 12 and 13 . FIG. 14is a state diagram illustrating generation powertrain states of a PHESsystem, including PHES system 1000, according to an example embodiment.

The states in FIG. 14 occur sequentially, for the most part, andcorrespond to startup and grid synchronization of the generationpowertrain. The preferred sequential relationship of these states, withexpected allowable transitions, is indicated by directional arrowsbetween states.

At GPT Base state 1048, the generation powertrain is not driven. It istypically not spinning (i.e., at zero RPM), but it may still be spinningas it comes into this state from another state in which it was spinningBoth generation circuit breakers (e.g., 211, 212) are open. Thegeneration powertrain is ready to be spun.

At GPT Spin Up state 1050, the generation powertrain is connected to,and driven by, the VFD, spinning up to rated speed. For gridconnections, once at grid speed, the generator (e.g., generation system230) may not yet be synchronized to the external electrical grid.

GPT Generation state 1052, is a typical operating state for thegeneration mode 1004. At this state, the generation powertrain isspinning at rated speed (i.e., steady state) and the circuit breaker tothe grid is closed. The generation powertrain is connected to the grid.

GPT Slow Roll state 1054, is a typical state for the generationpowertrain when the PHES system is in charge mode 1002, unless the GPTsystem has cooled to the point that it can be in the base state. At thisstate, the generation powertrain is spinning at a low speed (i.e., slowrolling). A generation turning motor (e.g., 221-1) is on to maintain theslow rotational speed of the generation powertrain.

The generation powertrain states illustrated in FIGS. 12, 13, and 14 canbe further described with respect to the electrical status of the powerinterface 2002. Table I lists power interface 2002 component status forGPT states illustrated in FIGS. 12, 13, and 14 .

TABLE 1 Status GPT GPT GPT GPT Base Spin Up Generation Slow Roll 10481050 1052 1054 VFD 214 Off On Off Off VFD-to-GEN Open Closed Open OpenBreaker 211 GEN grid-connect Open Open Closed Open Breaker 212 GENTurning Motor Off Off Off On 221-1

Transitions between generation powertrain states are described in thefollowing paragraphs, with steps recited in preferred sequence.Component references refer to example embodiment GPT system 200, but thesteps may be applied to other configurations to accomplish the samestate transitions.

GPT Base 1048 to GPT Spin Up 1050. For this state transition, theworking fluid loop valving configuration and pressure must be at theright state before this transition can take place, as described belowwith respect to GPTV states. Power is first applied to a motor to spinthe generation powertrain. In GPT system 200, VFD-to-generator breaker211 is closed and VFD 214 is turned on, resulting in the generationpowertrain spinning. Generator 210-1 is acting as a motor and acceptingcurrent from VFD 214. Compressor 230-1 and turbine 240-1 are spinning.The motor speed is then increased via VFD 214, bringing the generationpowertrain up to a grid-synchronous speed.

GPT Spin Up 1050 to GPT Generation 1052. This transition is agrid-synchronization transition. Motor (e.g., generator 210-1 acting asa motor) speed is adjusted through current control (e.g., at VFD 214) toensure grid-synchronous speed and to prevent speed overshoot. Motorphase is adjusted (e.g., at VFD 214) until the motor phase is gridsynchronous. Power supply from grid to motor is shutoff (e.g.,grid-connect breaker 212 is closed), and the motor then acts as agenerator to supply power to the grid (e.g., VFD-to-generator breaker211 is opened). The VFD will then start powering down to zero.

GPT Generation 1052 to GPT Base 1048. This transition can happen, forexample, during both normal shutdown of the generation powertrain andduring a trip event. Power supply from grid to motor is opened (e.g.,grid-connect breaker 212 is opened). Once the generation powertrain hastransitioned into GPT Base 1048 (after opening of the breaker), thegeneration powertrain will still be spinning, and will start rampingdown to zero speed unless the powertrain is further transitioned to theGPT Slow Rolling 1054 state prior to spinning down to zero.

GPT Spin Up 1050 to GPT Base 1048. This transition could happen, forexample, due to a trip signal. The VFD (e.g., VFD 214) is turned off andno longer connected to the generator (e.g., VFD-to-generator breaker 211is opened). Once the generation powertrain has transitioned into GPTBase 1048 (after opening of the breaker), the generation powertrain willstill be spinning, and will start ramping down to zero speed unless thegeneration powertrain is further transitioned to the GPT Slow Rolling1054 state prior to spinning down to zero

GPT Base 1048 to GPT Slow Rolling 1054. This transition takes place byturning on the turning motor (e.g., turning motor 221-1), which turnsthe drive train (e.g., generation turbomachinery 230-1, 240-1) at a verylow, “slow rolling speed” (e.g., 0.1% to 1%, 1% to 5%, or 5% to 10% ofsteady state generation RPM). In normal operation, as the drive trainramps down in speed, the turning motor will be turned on during rampdown to ensure the speed of the turbomachinery drivetrain does not slowdown below the slow rolling speed, or if the speed slows below the slowrolling speed, then it is brought back to the slow rolling speed. Thiscan be accomplished through an overrunning clutch (e.g., overrunningclutch 221-2) connected between the turning motor and the drivetrainthat disengages when the driver side (e.g. drivetrain) of the clutch isoperating at speeds higher than the slow rolling speed, and engages whenthe driver side of the clutch is operating at speeds lower than or equalto the slow rolling speed. This results in the turning motor engagingwith the turbine when the turbine reaches the speed of the turningmotor. The motor will then maintain the slow rolling speed.

GPT Slow Rolling 1054 to GPT Base 1048. The turning motor (e.g., turningmotor 221-1) is turned off. The generation powertrain will subsequentlycoast down to substantially zero rpm.

GPT Slow Rolling 1054 to GPT Spin Up 1050. To start the generationstartup process with the generation powertrain spinning, the powertraincan transition directly from GPT Slow Rolling 1054 to GPT Spin Up 1050by sequentially connecting the VFD to the generator (acting as a motor)(e.g., closing VFD-to-generator breaker 211) and turning off the turningmotor (e.g., turning motor 221-1).

The generation powertrain transitional states illustrated in FIGS. 12and 13 can also be further described with respect to the valve statesassociated with generation powertrain, including, for example, bypassand recirculation loops.

FIG. 16 is a state diagram illustrating generation powertrain (e.g., GPTsystem 200) valve states (i.e., GPTV states), of a PHES system,including PHES system 1000, from a generation powertrain perspective(e.g., GPT system 200 and associated GPT system 200 bypass/recirculationvalves), according to an example embodiment.

The states in FIG. 16 occur sequentially, for the most part. Thepreferred sequential relationship of these states, with expectedallowable transitions, is indicated by directional arrows betweenstates.

At GPTV Base state 1064, the valves are configured to have bothrecirculation valves and the bypass valves open. This is considered afail-safe state.

At GPTV Recirculation state 1070, the generation working fluid valvesare configured such that they can provide working fluid circulation andany desired heat removal for the generation powertrain (e.g., GPT system200) as it spins at a low rate (e.g., slow rolling speed). Thegeneration powertrain is also isolated from the high-pressure side ofthe working fluid loop (e.g., working fluid loop 300).

At GPTV Bypassed state 1066, the bypass valve is open in addition to theisolation (shutoff) valves. This allows working fluid to bypass thegeneration turbine partially, which allows the control of the turbinepower generation prior to reaching full speed and closing the breaker.Beneficially, this allows the use of a uni-directional VFD (e.g., VFD214).

At GPTV HP Connected state 1068, the generation working fluid valves areconfigured such that working fluid can be circulated between thehigh-pressure side and the low-pressure side via the generationpowertrain. All the working fluid bypass loops are closed to preventloss. Valve 229 is closed but may be in a state where it is ready to beopened quickly to help with anti-surge as necessary in case of a tripevent.

Table II lists valve status for state transitions illustrated in FIGS.12 and 13 and GPTV states illustrated in FIG. 16 .

TABLE II Status GPTV GPTV GPTV GPTV Base Recirculation Bypassed HPConnected 1064 1070 1066 1068 Compressor Shutoff Closed Closed Open OpenValve 231 (fails closed) Turbine Shutoff Closed Closed Open Open Valve241 (fails closed) Compressor Bypass Open Closed Open Closed Valve 229(fails open) Compressor Recirc Open Open Closed Closed Valve 232 (failsclosed) Turbine Recirc Open Open Closed Closed Valve 242 (fails open)Bypass Path Closed Closed Closed Closed Valve 222 (fails open) BypassPath Closed Closed Closed Closed Valve 401

Further illustrating the GPTV states, FIGS. 3A, 3B, 3C, and 3D eachillustrate a portion of FIG. 3 encompassing GPT system 200 andassociated bypass/recirculation valves, each according to an exampleembodiment. FIG. 3A illustrates GPTV base state 1064. FIG. 3Billustrates GPTV Bypass state 1066. FIG. 3C illustrates GPTVRecirculation state 1070. FIG. 3D illustrates GPTV HP Connected state1068. Valve positions are indicated in FIGS. 3A, 3B, 3C, and 3D with afilled valve icon representing a closed valve and an unfilled valve iconrepresenting an open valve. For example, in FIG. 3A, valve 231 is closedand valve 232 is open.

Transitions between generation powertrain valve (GPTV) states aredescribed in the following paragraphs, with steps recited in preferredsequence. Component references refer to example embodiments GPT system200 and working fluid loop 300, but the steps may be applied to otherconfigurations to accomplish the same GPTV state transitions.

GPTV Base 1064 to GPTV Recirculation 1070. Turbine bypass fluid path isclosed (e.g., valve 229 is closed).

GPTV Base 1064 to GPTV Bypassed 1066. Compressor recirculation fluidpath and turbine recirculation fluid path are closed (e.g., valve 232and valve 242 are closed). Turbine bypass fluid path (e.g., valve 229)remains open to allow working fluid to go through the bypass loop.Compressor outlet (shutoff) valve 231 is opened. Turbine inlet (shutoff)valve 241 is opened.

GPTV Bypassed 1066 to GPTV HP Connected 1068. Turbine bypass fluid pathis closed (e.g., valve 229 is closed).

GPTV Bypassed 1066 to GPTV Base 1064. Generation powertrainrecirculation fluid paths are opened (e.g., recirculation valves 232,242 are opened). Turbine inlet fluid paths are closed (e.g., valve 241is closed). Compressor outlet fluid path is closed (e.g., valve 231 isclosed).

GPTV HP Connected 1068 to GPTV Base 1064. This transition can happen,for example, due to a trip event. Turbine inlet fluid paths are quicklyclosed (e.g., valve 241 is quickly closed). Turbine bypass fluid path isquickly opened (e.g., valve 229 is quickly opened) to help withanti-surge. Compressor outlet fluid path is closed (e.g., valve 231 isclosed). Generation powertrain recirculation fluid paths are opened(e.g., recirculation valves 232, 242 are opened).

GPTV HP Connected 1068 to GPTV Bypassed 1066. This transition generallyhappens during normal shut down. Turbine bypass fluid path is opened(e.g., valve 229 is opened) to help with anti-surge.

GPTV Recirculation 1070 to GPTV Base 1064. Turbine bypass fluid path isopened (e.g., valve 229 is opened).

D. States of Charge Powertrain and Associated Valves

FIG. 15 is a state diagram illustrating charge powertrain (e.g., CPTsystem 100) states (i.e., CPT states) of a PHES system, including PHESsystem 1000, according to an example embodiment.

The states in FIG. 15 occur sequentially, for the most part. Thepreferred sequential relationship of these states, with expectedallowable transitions, is indicated by directional arrows betweenstates.

At CPT Base state 1056, the charge powertrain is not driven. It istypically not spinning (i.e., at zero RPM), but it may still be spinningas it comes into this state from another state in which it was spinningBoth charge circuit breakers (e.g., 111, 112) are open. The chargepowertrain is ready to be spun.

At CPT Spin Up state 1058, the charge powertrain is connected to, anddriven by, the VFD, spinning up to rated speed. For grid connections,once at grid speed, the motor (e.g., charge motor system 110) is not yetsynchronized to the external electrical grid.

CPT Charge state 1060, is a typical operating state for the charge mode1002. At this state, the charge powertrain is spinning at rated speed(i.e., steady state) and the circuit breaker to the grid is closed. Thecharge powertrain is connected to the grid.

CPT Slow Rolling state 1062, is a typical state for the chargepowertrain when the PHES system is in generation mode 1004, unless theCPT system has cooled to the point that it can be in the base state. Atthis state, the charge powertrain is spinning at a very low, “slowrolling speed” (e.g., 0.1% to 1%, 1% to 5%, or 5% to 10% of steady statecharge RPM). A charge turning motor (e.g., 121-1) is on to maintain theslow rolling speed of the charge powertrain.

The charge powertrain states illustrated in FIG. 15 can be furtherdescribed with reference to the electrical status of the power interface2002, illustrated in FIG. 9 , which can control electrical power in theCPT system 100. Table III lists power interface 2002 component status,and charge turning motor, for CPT states illustrated in FIG. 15 .

TABLE III Status CPT CPT CPT CPT Base Spin Up Charge Slow Roll VFD 214Off On Off Off VFD-to-CHG-Motor Open Closed Open Open Breaker 111 CHGMotor Grid-connect Open Open Closed Open Breaker 112 CHG Turning MotorOff Off Off On 121-1

Transitions between charge powertrain states are described in thefollowing paragraphs, with steps recited in preferred sequence.Component references refer to example embodiment CPT system 100 andpower interface 2002, but the steps may be applied to otherconfigurations to accomplish the same state transitions.

CPT Base 1056 to CPT Spin Up 1058. For this state transition, theworking fluid loop valving configuration and pressure must be at theright state before this transition can take place, as described belowwith respect to CPTV states. Power is first applied to a motor (e.g.,motor 110-1) to spin the charge powertrain. For CPT system 100,VFD-to-motor breaker 111 is closed and VFD 214 is turned on, resultingin the charge powertrain spinning Compressor system 1301 and turbinesystem 140 are spinning. The motor speed is then increased via VFD 214,bringing the generation powertrain up to a grid-synchronous speed.

CPT Spin Up 1058 to CPT Charge 1060. This transition is agrid-synchronization transition. Motor (e.g., motor 110-1) speed isadjusted through current control (e.g., at VFD 214) to ensuregrid-synchronous speed and to prevent speed overshoot. Motor phase isadjusted (e.g., at VFD 214) until the motor phase is grid synchronous.Power supply from grid to motor is activated (e.g., grid-connect breaker112 is closed), and VFD power to motor is stopped (e.g., VFD-to-motorbreaker 111 is opened). The VFD will then start powering down to zero.

CPT Charge 1060 to CPT Base 1056. This transition happens, for example,during both normal shutdown of the charge powertrain and during a tripevent. Power supply from grid to motor is halted (e.g., grid-connectbreaker 112 is opened). Once the charge powertrain has transitioned intoCPT Base 1056 (upon the opening of the breaker), the charge powertrainwill still be spinning, and will start ramping down to zero speed unlessthe powertrain is further transitioned to the CPT Slow Rolling 1062state prior to spinning down to zero.

CPT Spin Up 1058 to CPT Base 1056. This transition could happen, forexample, due to a trip signal. The VFD (e.g., VFD 214) is turned off andno longer connected to the motor (e.g., VFD-to-motor breaker 111 isopened). Once the charge powertrain has transitioned into CPT Base 1056(upon the opening of the breaker), the charge powertrain will still bespinning, and will start ramping down to zero speed unless the chargepowertrain is further transitioned to the CPT Slow Rolling 1062 stateprior to spinning down to zero

CPT Base 1056 to CPT Slow Rolling 1062. This transition takes place byturning on the turning motor (e.g., turning motor 121-1), which turnsthe drivetrain (e.g., charge turbomachinery 130-1, 140-1) at a low speed(e.g., slow rolling speed). In normal operation, as the drivetrain rampsdown in speed, the turning motor will be turned on during ramp down toensure the speed of the drivetrain does not slow down below the minimumspeed, or if the speed slows below the minimum speed, then it is broughtback to the minimum speed. This can be accomplished through anoverrunning clutch (e.g., overrunning clutch 121-2) connected betweenthe turning motor and the drivetrain that disengages when the driverside (e.g., drivetrain) of the clutch is operating at speeds higher thana minimum speed (e.g., slow rolling speed), and engages when the driverside of the clutch is operating at speeds lower than or equal to aminimum speed (e.g., slow rolling speed). This results in the turningmotor engaging with the turbine when the turbine reaches the speed ofthe turning motor. The motor will then maintain the low (e.g., slowrolling) speed.

CPT Slow Rolling 1062 to CPT Base 1056. The turning motor (e.g., turningmotor 121-1) is turned off. The charge powertrain will subsequentlycoast down to zero rpm.

CPT Slow Rolling 1062 to CPT Spin Up 1058. To start the charge startupprocess with the charge powertrain spinning, the powertrain cantransition directly from CPT Slow Rolling 1062 to CPT Spin Up 1058 bysequentially connecting the VFD to the motor (e.g., closing VFD-to-motorbreaker 111) and turning off the turning motor (e.g., turning motor121-1).

Charge powertrain transitional states can also be further described withrespect to the valve states associated with charge powertrain bypass andrecirculation loops.

FIG. 17 is a state diagram illustrating charge powertrain (e.g., CPTsystem 100) valve states (i.e., CPTV states), of a PHES system,including PHES system 1000, from a charge powertrain perspective (e.g.,CPT system 100 and associated CPT system 100 bypass/recirculationvalves), according to an example embodiment.

The states in FIG. 17 occur sequentially, for the most part. Thepreferred sequential relationship of these states, with expectedallowable transitions, is indicated by directional arrows betweenstates.

At CPTV Base state 1072, the valves are configured to have bothrecirculation valves and the bypass valves open. This is considered afail-safe state.

At CPTV Recirculation state 1078, the generation working fluid valvesare configured such that they can provide working fluid circulation andany desired heat removal for the charge powertrain (e.g., CPT system100) as it spins at a slow rate (e.g., slow rolling speed). The chargepowertrain is also isolated from the high-pressure side of the workingfluid loop.

At CPTV Bypassed state 1074, the bypass valve is open in addition to theisolation valves. This allows working fluid to circulate via a bypassloop to reduce load on the charge compressor (e.g., compressor system130).

At CPTV HP Connected state 1076, the charge working fluid valves areconfigured such that working fluid can be circulated between thehigh-pressure side and the low-pressure side via the charge powertrain.All the working fluid bypass loops are closed to prevent loss. Valve 119is closed but in a state where it is ready to be opened quickly to helpwith anti-surge as necessary in case of a trip event.

Table IV lists valve status for CPTV states illustrated in FIG. 17 .

TABLE IV Status CPTV CPTV CPTV CPTV HP Base Recirculation BypassedConnected Valve 1072 1078 1074 1076 Compressor Shutoff Closed ClosedOpen Open Valve 131 (fails closed) Turbine Shutoff Closed Closed OpenOpen Valve 141 (fails closed) Compressor Bypass Open Closed Open ClosedValve 119 (fails closed) Compressor Recirc Open Open Closed Closed Valve132 (fails closed) Turbine Recirc Open Open Closed Closed Valve 142(fails open)

Further illustrating the CPTV states, FIGS. 3E, 3F, 3G, and 3H eachillustrate a portion of FIG. 3 encompassing CPT system 100 andassociated bypass/recirculation valves, each according to an exampleembodiment. FIG. 3E illustrates CPTV base state 1072. FIG. 3Fillustrates CPTV Bypass state 1074. FIG. 3G illustrates CPTVRecirculation state 1078. FIG. 3H illustrates CPTV HP Connected state1076. Valve positions are indicated in FIGS. 3E, 3F, 3G, and 3H with afilled valve icon representing a closed valve and an unfilled valve iconrepresenting an open valve. For example, in FIG. 3E, valve 131 is closedand valve 132 is open.

Transitions between charge powertrain valve (CPTV) states are describedin the following paragraphs, with steps recited in preferred sequence.Component references refer to example embodiments CPT system 100 andworking fluid loop 300, but the steps may be applied to otherconfigurations to accomplish the same CPTV state transitions.

CPTV Base 1072 to CPTV Recirculation 1078. Compressor high-flowrecirculation fluid path is closed (e.g., valve 119 is closed).

CPTV Base 1072 to CPTV Bypassed 1074. Compressor recirculation fluidpath and turbine recirculation fluid path are closed (e.g., valve 132and valve 142 are closed). Compressor high-flow recirculation fluid path(e.g., valve 119) remains open to allow working fluid to go through therecirculation loop. Compressor outlet valve 131 is opened. Turbine inletvalve 141 is opened.

CPTV Bypassed 1074 to CPTV HP Connected 1076. Compressor high-flowrecirculation fluid path is closed (e.g., valve 119 is closed).

CPTV Bypassed 1074 to CPTV Base 1072. Charge powertrain recirculationfluid paths are opened (e.g., recirculation valves 132, 142 are opened).Turbine inlet fluid path is closed (e.g., valve 141 is closed).Compressor outlet fluid path is closed (e.g., valve 131 is closed).

CPTV HP Connected 1076 to CPTV Base 1072. This transition may happen,for example, due to a trip event. Turbine inlet fluid path is quicklyclosed (e.g., valve 141 is quickly closed). Compressor high-flowrecirculation fluid path is quickly opened (e.g., valve 119 is quicklyopened) to help with anti-surge. Compressor outlet fluid path is closed(e.g., valve 131 is closed). Charge powertrain recirculation fluid pathsare opened (e.g., recirculation valves 132, 142 are opened).

CPTV HP Connected 1076 to CPTV Bypassed 1074. This transition canhappen, for example, during normal shut down or during a grid tripevent. Compressor high-flow recirculation fluid path is opened (e.g.,valve 119 is opened) to help manage the pressure ratio across thecompressor and avoid compressor surge.

CPTV Recirculation 1078 to CPTV Base 1072. Compressor high-flowrecirculation fluid path is opened (e.g., valve 119 is opened).

E. States of Ambient Heat Exchanger and Associated Valves

FIG. 18 is a state diagram illustrating ambient cooler (also referred toas ambient heat exchanger) states (e.g., AHX system 700) of a PHESsystem, including PHES system 1000, according to an example embodiment.The two states in FIG. 18 can transition back-and-forth, as indicated bydirectional arrows between the states.

Example ambient cooler states include, Ambient Cooler Bypassed 1080,Ambient Cooler Active 1082, and Ambient Cooler Off 1084. During AmbientCooler Off 1084, working fluid loop valves regulating working fluid flowpaths into or out of the ambient cooler (e.g., AHX system 700) are allclosed, preventing movement of working fluid into or out of the ambientcooler. Ambient cooler fans, if present, are off. During Ambient CoolerBypassed 1080, working fluid loop valves are configured such that theambient cooler is bypassed by working fluid circulating in the workingfluid loop (e.g. working fluid loop 300). Ambient cooler fans, ifpresent, are off. During Ambient Cooler Active 1082, working fluid loopvalves are configured such that working fluid in the working fluid loopcan enter the ambient cooler. If the working fluid is actuallycirculating through the ambient cooler, the ambient cooler removes heatfrom working fluid in the working fluid loop and exhausts it theenvironment; this state may, for example, be used during generation mode1004 and the bypass state 1080 may, for example, be used during chargemode 1002. Ambient cooler fans, if present, may be used to vary the rateof heat extraction from the working fluid. Ambient cooler fans may beturned on, and may have their speed adjusted, when working fluid isactively circulating through the ambient cooler, and the fans may beturned off if the working fluid is not actively circulating through theambient cooler, regardless of valve configuration.

Alternatively, in other embodiments of PHES systems and/or working fluidloop, an ambient cooler (e.g., AHX system 700) can be configured to becontinuously connected to the working fluid loop (i.e., no bypass stateis available). In these alternative embodiments, the fans or otherequipment (e.g., heat sink fluid flow rate) are used to vary the heatremoval capability of the ambient cooler. For example, during generationmode 1004, ambient cooler fans are turned on to actively remove heatfrom the working fluid, and during generation mode 1002, when ambientcooler fans are turned off, the ambient cooler does not passively removea significant amount of heat from the working fluid.

Table V lists cooler and valve status for ambient cooler (e.g., AHXsystem 700) states illustrated in FIG. 18 .

TABLE V Status Ambient Cooler Ambient Cooler Ambient Cooler BypassedActive Off 1080 1082 1084 Bypass Open Closed Closed Valve 323 Cold-sideIsolation Closed Open Closed Valve 324 Recuperator-side Closed OpenClosed Isolation Valve 325 AHX Fans Fan Off Fan On Fan Off

Further illustrating ambient cooler states 1080 and 1082, FIGS. 3I and3J each illustrate a portion of FIG. 3 encompassing AHX system 700 andassociated bypass valves, according to an example embodiment. FIG. 3Iillustrates ambient cooler bypass state 1080. FIG. 3J illustratesambient cooler active state 1082. Valve positions are indicated in FIGS.3I and 3J with a filled valve icon representing a closed valve and anunfilled valve icon representing an open valve. For example, in FIG. 3I,valve 324 is closed and valve 323 is open.

In an alternative valve arrangement for the ambient cooler states 1080and 1082, FIGS. 3K and 3L each illustrate a portion of FIG. 3 , but withvalve 325 removed. FIG. 3K illustrates ambient cooler bypass state 1080.FIG. 3L illustrates ambient cooler active state 1082. Valve positionsare indicated in FIGS. 3K and 3L with a filled valve icon representing aclosed valve and an unfilled valve icon representing an open valve. Forexample, in FIG. 3K, valve 324 is closed and valve 323 is open. Thevalve states in Table V are applicable to both FIGS. 3I, 3J and FIGS.3K, 3L, with the exception that valve 325 states are not applicable toFIGS. 3K, 3L.

Transitions between ambient cooler states are described in the followingparagraphs, with steps recited in preferred sequence. Componentreferences refer to example embodiments of AHX system 700 and workingfluid loop 300, but the steps may be applied to other configurations toaccomplish the same ambient cooler state transitions.

Ambient Cooler Bypassed 1080 to Ambient Cooler Active 1082. Thistransition may occur, for example, for mode switch from charge mode 1002to generation mode 1004 or from start up (e.g., cold dry standby mode1010) to hot standby 1024. Isolation valves 324 and 325 (if present) areopened. Bypass valve 323 is closed. If working fluid is circulatingthrough the ambient cooler (e.g. AHX system 700), fans (e.g., fans inAHX system 700) are turned on and fan speed may be controlled fordesired heat removal.

Ambient Cooler Active 1082 to Ambient Cooler Bypassed 1080. Thistransition may occur, for example, for mode switch from generation mode1004 to charge mode 1002. Isolation valves 324 and 325 (if present) areclosed. Bypass valve 323 is opened. Fans (e.g., fans in AHX system 700)are turned off.

Ambient Cooler Active 1082 to Ambient Cooler Off 1084. This transitionmay occur, for example, for mode switch from hot standby 1008 and/or1024 to cold dry standby 1010 and/or 1030. Isolation valves 324 and 325(if present) are closed. Bypass valve 323 is closed. Fans (e.g., fans inAHX system 700) are turned off.

F. States and Control of Inventory Control System

The working fluid inventory control system (ICS) is part of the workingfluid loop subsystem (e.g., working fluid loop 300). The inventorycontrol system may include a compressor, a filtering system to conditionthe working fluid, one or more working fluid tanks, fluid paths, andvalves to manage the various requirements from this system.

Example components of an ICS 390 embodiment, as implemented in workingfluid loop 300, are shown in FIG. 3M. FIG. 3M illustrates a portion ofFIG. 3 encompassing an inventory control system, according to an exampleembodiment.

As illustrated in FIG. 24 , one or more control systems may be used tocontrol ICS system 390. A PHES supervisory controller 1124 may determineand/or direct PHES system 1000 modes and/or states, which may includeICS system 390 modes and/or states. Alternatively or additionally, anICS controller 1125 may receive directives from PHES supervisorycontroller 1124, responsively enact changes in ICS 390, and reportconditions to PHES supervisory controller 1124. For example, a powerdemand signal can be sent from PHES supervisory controller 1124 to ICScontroller 1125. The ICS controller 1125 may then determine valvesequences and operations based, for example, on current PHES systemconditions and the power demand signal. Alternatively or additionally,PHES supervisory controller 1124 may enact changes in ICS 390. Forexample, PHES supervisory controller 1124 may determine a new powerdemand level in the PHES system 1000 and responsively direct valvesequences and operations based, for example, on current PHES systemconditions and power requirements, to reach that power demand level.

During normal operation, in order to increase power in the PHES system1000, a controller (e.g., controller 1125 and/or controller 1124) canincrease the working fluid pressure. To accomplish this, the controllercan cause the following:

-   -   Open valve 312 to throttle working fluid from low-pressure tank        system 310 into the low-pressure side of the working fluid loop        300. This increases the inlet pressure into the CPT system 100        or GPT system 200, which will, in turn, increase the power of        the PHES system 1000.    -   Determine current PHES system 1000 power level and compare to        the power demand level. This step may be repeated until: (i) the        current power level matches the demand level, or (ii) there is        no more driving head (the pressure in low-pressure tank system        310 is only marginally above the working fluid loop 300 low-side        pressure). The latter stop condition can be determined, for        example, by comparing low-pressure tank system 310 pressure and        working fluid loop 300 low-side pressure, or by determining that        current power levels have ceased increasing. If either of these        stop conditions are met, close valve 312.    -   Determine if further power increase is still required (i.e., the        second stop condition above occurred prior to reaching demand        level). If further power increase is required, open valve 322 to        add working fluid from the high-pressure tank system 320 into        the low-pressure side of the working fluid loop 300. This can be        continued until the PHES system 1000 reaches the demand power        level. The ICS tank systems 310, 320 are preferably sized such        that the PHES system 1000 can get to full power in either charge        mode 1002 or generation mode 1004.

To decrease the power in the PHES system 1000, a controller (e.g.,controller 1125 and/or controller 1124) can decrease the working fluidpressure. To accomplish this, the controller can cause the following:

-   -   Open valve 321 to throttle working fluid from the high-pressure        side of the working fluid loop 300 into high-pressure tank        system 320. This decreases the inlet pressure into the CPT        system 100 or GPT system 200, which will, in turn, decrease the        power of the PHES system 1000.    -   Determine current PHES system 1000 power level and compare to        the power demand level. This step may be repeated until: (i) the        current power level matches the demand level, or (ii) there is        no more driving head (high-pressure side of the working fluid        loop 300 is only marginally above the pressure in high-pressure        tank system 320). The latter stop condition can be determined,        for example, by comparing high-pressure tank system 320 pressure        and working fluid loop 300 high-side pressure, or by determining        that current power levels have ceased decreasing. If either of        these stop conditions are met, close valve 321.    -   Determine if further power decrease is still required (i.e., the        second stop condition above occurred prior to reaching demand        level). If further power decrease is required, open valve 311 to        add working fluid from the high-pressure side of the working        fluid loop 300 into the low-pressure tank system 310. This can        be continued until the PHES system 1000 reaches the demand power        level. The ICS tank systems 310, 320 are preferably sized such        that the system can get to minimum power in either charge mode        1002 or generation mode 1004.

Other functions ICS controller 1125 can perform include bringing theworking fluid loop 300 pressures to a desired pressure (e.g., base,ambient, P_(standby), specific pressure range(s) that are below eitheror both the current pressures in the working fluid high-side fluid pathsand low-side fluid paths) following a normal shutdown or a trip event sothat the PHES system can be restarted.

Following a trip event, a controller (e.g., controller 1125 and/orcontroller 1124) can cause the following:

-   -   Open valve 318 to bleed working fluid from high-pressure working        fluid paths into low-pressure tank system 310. By using large        valve 318 (instead of or in addition to valve 311), this can        reduce the pressure in the high-pressure working fluid paths at        a rate fast enough to help maintain a settle-out pressure below        a threshold limit.    -   Close valve 318 once pressure in low-pressure tank system 310 is        substantially equal to that of the high-pressure working fluid        paths.    -   Open valve 305 and then turn on compressor 303 to draw working        fluid from high-pressure working fluid paths into high-pressure        tank system 320 until the high-pressure working fluid paths are        within a desired high-pressure range.    -   Turn off compressor 303 and then close valve 305.    -   Open valve 304 and then turn on compressor 303 to draw working        fluid from low-pressure working fluid paths into the        high-pressure tank system 320 until the low-pressure working        fluid paths are within a desired low-pressure range.

If the PHES system 1000 is shut down normally, large valve 318 may notneed to be opened because the pressure in the high-pressure workingfluid paths has been slowly reduced during the process to substantiallya base level. Accordingly, a controller (e.g., controller 1125 and/orcontroller 1124) can cause the following:

-   -   Open valve 305 and then turn on compressor 303 to draw working        fluid from high-pressure working fluid paths into high-pressure        tank system 320 until the pressure in high-pressure working        fluid paths are at a base pressure.    -   Turn off compressor 303 and then close valve 305.    -   Open valve 304 and then turn on compressor 303 to draw working        fluid from low-pressure working fluid paths into the        high-pressure tank system 320 until the low-pressure working        fluid paths are at a base pressure. This should take only a        short time because the low-pressure working fluid paths should        already be very close to base pressure.

If the working fluid loop 300 leaks working fluid, to controller (e.g.,controller 1125 and/or controller 1124) can cause additional workingfluid to be added to the working fluid loop 300 as follows. Steps aredescribed as if from a state where all referenced valves are initiallyclosed:

-   -   Open valve 302.    -   Turn on compressor 303 to add working fluid from ambient air        when air is the working fluid or from an external working fluid        make-up reservoir (not shown) into high-pressure tank system 320        until high-pressure tank system 320 reaches a desired pressure.    -   Turn off compressor 303.    -   Close valve 302.    -   Open valve 322 to add working fluid from high-pressure tank        system 320 to low-pressure working fluid paths.    -   Close valve 322.    -   Repeat above steps until the working fluid loop pressure is at a        desired level.        G. States of Hot-Side Loop

FIG. 25 is a state diagram illustrating hot-side loop (also referred toas HTS loop) states of a PHES system, including PHES system 1000,according to an example embodiment. The hot-side loop is the flow pathof circulating HTS medium 590, for example, through HTS system 501 inFIG. 4 and, in some states, HHX system 500 in FIGS. 2, 3, 6A, and 6B.

The states in FIG. 25 occur sequentially, for the most part. Thepreferred sequential relationships of these states are indicated bydirectional arrows between states.

At Drained state 1146, HTS medium 590 in fluid paths, including heatexchangers, has been drained or is being drained into the HTS tanks(e.g., 510 and/or 520). Heat trace 560 is off. When coming out ofdrained state 1146, e.g., to standby state 1138, heat trace 560 may beturned on prior to reintroduction of HTS medium 590 into fluid paths.

At Standby state 1138, the hot-side loop is filled or filling with HTSmedium 590 and is ready for HTS medium 590 to flow. If the loop is notalready filled, then a small flow rate would be temporarily establishedin the appropriate direction in order to fill the fluid paths with HTSmedium 590.

At Flow-to-Hot state 1140, the hot-side loop is configured to allow HTSmedium 590 flow from warm HTS system 591 to hot HTS system 592 (e.g.,from warm HTS tank 510 to hot HTS tank 520 in HTS system 501) via thehot-side heat exchanger(s) (e.g., HHX system 500). Warm pump 530 is onto deliver this flow. Heat trace 560 may be turned off because HTSmedium 590 is already hot. Bypass valve 551 is closed so that HTS medium590 flows through HHX system 500.

At Flow-to-Warm state 1142, the hot-side loop is configured to allow HTSmedium 590 flow from hot HTS system 592 to warm HTS system 591 (e.g.,from hot HTS tank 520 to warm HTS tank 510 in HTS system 501) via thehot-side heat exchanger(s) (e.g., HHX system 500). Hot pump 540 is on todeliver this flow. Heat trace 560 may be turned off because HTS medium590 is already hot. Bypass valve 551 is closed so that HTS medium 590flows through HHX system 500.

At Bypassed state 1144, HTS medium 590 is flowing in the hot-side looppreferably from hot HTS system 592 to warm HTS system 591 (e.g., fromhot HTS tank 520 to warm HTS tank 510 in HTS system 501), but notthrough the hot-side heat exchanger(s) (e.g., HHX system 500). Hot-sideheat exchanger(s) are bypassed by opening bypass valve 551 and closingisolation valves 555, 556. Alternatively, in another embodiment, HTSmedium 590 could flow in the hot-side loop from warm HTS system 591 tohot HTS system 592 (e.g., from warm HTS tank 510 to hot HTS tank 520 inHTS system 501), but not through the hot-side heat exchanger(s) (e.g.,HHX system 500).

Table VI lists equipment status for hot-side loop states illustrated inFIG. 25 . Component references refer to example embodiments illustratedin, for example, FIGS. 2, 3, 4, 6A, and 6B, and including HTS system 501and HHX system 500, but the status may be applied to otherconfigurations to accomplish the same hot-side loop state states.

TABLE VI Status Drained Standby Flow-to-Hot Flow-to-Warm Bypassed 11461138 1140 1142 1144 HX Bypass Closed Closed Closed Closed Open Valve 551Heat Trace 560 Off On Off Off Off Warm Pump 530 Off Off On Off *2 WarmHeater 512 *1 On On On On Warm Inflow Closed Closed Closed Open *3 Valve511 Warm Pump Outlet Closed Open Open Closed *2 Valve 557 HX WarmIsolation Closed Open Open Open Closed Valve 555 Warm Drain Open ClosedClosed Closed Closed Valve 552 Hot Pump 540 Off Off Off On *3 Hot Heater522 *1 On On On On Hot Inflow Closed Open Open Closed *2 Valve 521 HotPump Outlet Closed Closed Closed Open *3 Valve 558 HX Hot IsolationClosed Open Open Open Closed Valve 556 Hot Drain Open Closed ClosedClosed Closed Valve 553 *1 ON if HTS medium present; OFF if HTS mediumnot present *2 ON or OPEN if bypass flow to hot; OFF or CLOSED if bypassflow to warm *3 ON or OPEN if bypass flow to warm; OFF or CLOSED ifbypass flow to hotH. States of Cold-Side Loop

FIG. 26 is a state diagram illustrating cold-side loop (also referred toas CTS loop) states of a PHES system, including PHES system 1000,according to an example embodiment. The cold-side loop is the flow pathof circulating CTS medium 690, for example, through CTS system 601 inFIG. 5 and, in some states, CHX system 600 in FIGS. 2, 3, 6A, and 6B.

The states in FIG. 26 occur sequentially, for the most part. Thepreferred sequential relationship of these states are indicated bydirectional arrows between states.

At Drained state 1156, CTS medium 690 in fluid paths, including heatexchangers, has been drained or is being drained into the CTS tanks(e.g., 610 and/or 620), preferably into a warm CTS tank (e.g., warm CTStank 610). Preferably, no CTS pump is running once all CTS medium 690has been drained.

At Standby state 1148, the cold-side loop is filled or filling with CTSmedium 690 and is ready for CTS medium 690 to flow. Preferably, no CTSpump is running once the cold-side loop has been filled. If the loop isnot already filled, then a flow rate from pumps 630 and/or 640 would beestablished in the appropriate direction in order to fill the fluidpaths with CTS medium 690.

At Flow-to-Cold state 1150, the cold-side loop is configured to allowCTS medium 690 flow from warm CTS system 691 to cold CTS system 692(e.g., from warm CTS tank 610 to cold CTS tank 620 in CTS system 601)via the cold-side heat exchanger(s) (e.g., CHX system 600). Warm pump630 is on to deliver this flow. Cold pump 640, if bi-directional, canalso be on to assist with pressure control. Bypass valve 605 is closedso that CTS medium 690 flows through CHX system 600.

At Flow-to-Warm state 1152, the cold-side loop is configured to allowCTS medium 690 flow from cold CTS system 692 to warm CTS system 691(e.g., from cold CTS tank 620 to warm CTS tank 610 in CTS system 601)via the cold-side heat exchanger(s) (e.g., CHX system 600). Cold pump640 is on to deliver this flow. Warm pump 630, if bi-directional, canalso be on to assist with pressure control. Bypass valve 605 is closedso that CTS medium 690 flows through CHX system 600.

At Bypassed state 1154, CTS medium 590 is preferably flowing in thecold-side loop from cold CTS system 692 to warm CTS system (e.g., fromcold CTS tank 620 to warm CTS tank 610 in CTS system 601), but notthrough the cold-side heat exchanger(s) (e.g., CHX system 600).Cold-side heat exchanger(s) are bypassed by opening bypass valve 605 andclosing isolation valves 602, 603. Alternatively, in another embodiment,CTS medium 590 could flowing in the cold-side loop from warm CTS systemto cold CTS system 692 (e.g., from warm CTS tank 610 to cold CTS tank620 in CTS system 601), but not through the cold-side heat exchanger(s)(e.g., CHX system 600).

Table VII lists equipment status for cold-side loop states illustratedin FIG. 26 , in an embodiment of CTS system 601 where pumps 630, 640 areused for bi-directional pumping. Component references refer to exampleembodiments illustrated in, for example, FIGS. 2, 3, 5, 6A, and 6B andincluding CTS system 601 and CHX system 600, but the status may beapplied to other configurations to accomplish the same hot-side loopstates.

TABLE VII Status Drained Standby Flow-to-Cold Flow-to-Warm BypassedEquipment 1156 1148 1150 1152 1154 Bypass Valve Closed Closed ClosedClosed Open Valve 605 Inert Gas Purge *1 Closed Closed Closed ClosedValve 624 Cold Pump 640 Off Off On to Cold On to Warm *2 Cold IsolationClosed Open Open Open Closed Valve 602 Cold Tank Closed Open Open OpenOpen Valve 621 Cold Pump Isolation Closed Open Open Open Open Valve 641Cold Pump Bypass Closed Closed Closed Closed Closed Valve 642 Cold PumpIsolation Closed Open Open Open Open Valve 643 Warm Pump 630 Off Off Onto Cold On to Warm *2 Warm Isolation Closed Open Open Open Closed Valve603 Warm Tank Closed Open Open Open Open Valve 611 Warm Pump IsolationClosed Open Open Open Open Valve 631 Warm Pump Bypass Closed ClosedClosed Closed Closed Valve 632 Warm Pump Isolation Closed Open Open OpenOpen Valve 633 *1 OPEN until purge complete *2 ON-to-Warm if bypass flowto warm; ON-to-Cold if bypass flow to cold

Table VIII lists equipment status for cold-side loop states illustratedin FIG. 26 , in an embodiment of CTS system 601 where pumps 630, 640 arenot used for bi-directional pumping. Component references refer toexample embodiments illustrated in, for example, FIGS. 2, 3, 5, 6A, and6B and including CTS system 601 and CHX system 600, but the status maybe applied to other configurations to accomplish the same hot-side loopstates.

TABLE VIII Status Drained Standby Flow-to-Cold Flow-to-Warm Bypassed1156 1148 1150 1152 1154 Bypass Valve Closed Closed Closed Closed OpenValve 605 Inert Gas Purge *1 Closed Closed Closed Closed Valve 624 ColdPump 640 Off Off Off On to Warm *2 Cold Isolation Closed Open Open OpenClosed Valve 602 Cold Tank Closed Open Open Open Open Valve 621 ColdPump Isolation Closed Open Closed Open *5 Valve 641 Cold Pump BypassClosed Closed Open Closed *4 Valve 642 Cold Pump Isolation Closed OpenClosed Open *5 Valve 643 Warm Pump 630 Off Off On to Cold On to Warm *3Warm Isolation Closed Open Open Open Closed Valve 603 Warm Tank ClosedOpen Open Open Open Valve 611 Warm Pump Isolation Closed Open OpenClosed *4 Valve 631 Warm Pump Bypass Closed Closed Closed Open *5 Valve632 Warm Pump Isolation Closed Open Open Closed *4 Valve 633 *1 OPENuntil purge complete *2 On-to-Warm if bypass flow to warm; OFF if bypassflow to cold *3 On-to-Cold if bypass flow to cold; OFF if bypass flow towarm *4 OPEN if bypass flow to cold; CLOSED if bypass flow to warm *5CLOSED if bypass flow to cold; OPEN if bypass flow to warmIV. Use Cases

This section describes transient “use cases” that can be implemented ina PHES system, including PHES system 1000 and the subsystems describedherein. Each transient use case is a process or a transitionary sequencethat the PHES system undergoes, and can be described by mode and/orstate changes.

A. Cold Dry Standby to Hot Standby (PHES System Startup)

This use case is illustrated in FIG. 10 as the transition from Cold DryStandby mode 1010 to Hot Standby mode 1008, and in FIG. 11 as thetransition from operating state 1030 to operating state 1024.

B. Hot Standby to Charge (PHES System Startup)

This use case is illustrated in FIG. 10 as the transition from HotStandby mode 1008 to Charge mode 1002, and in FIG. 11 as the transitionfrom operating state 1024 to operating state 1014.

FIG. 19 further illustrates this use case. FIG. 19 is a state diagramillustrating operating and transitional states in a PHES system,including PHES system 1000, according to an example embodiment. Theseare example state transitions and other embodiments are possible aswell. FIG. 19 illustrates transition from the HOT STANDBY state 1024 toCHARGE (GPT BASE) state 1014, with intermediate transitional states1086, 1088, 1090 occurring sequentially in between. Each of thesubsystem states is described elsewhere herein.

C. Hot Standby to Generation (PHES System Startup)

This use case is illustrated in FIG. 10 as the transition from HotStandby mode 1008 to Generation mode 1004, and in FIG. 11 as thetransition from operating state 1024 to operating state 1016.

FIG. 20 further illustrates this use case. FIG. 20 is a state diagramillustrating operating and transitional states in a PHES system,including PHES system 1000, according to an example embodiment. Theseare example state transitions and other embodiments are possible aswell. FIG. 20 illustrates transition from the HOT STANDBY state 1024 toGENERATION (CPT BASE) state 1016, with intermediate transitional states1094, 1096, 1098 occurring sequentially in between. Each of thesubsystem states is described elsewhere herein.

D. Charge to Hot Turning (PHES System Shutdown)

This use case is illustrated in FIG. 10 as the transition from Chargemode 1002 to Hot Turning mode 1006, and in FIG. 11 as the transitionfrom operating state 1014 to operating state 1018.

FIG. 21 further illustrates this use case. FIG. 21 is a state diagramillustrating operating and transitional states in a PHES system,including PHES system 1000, according to an example embodiment. Theseare example state transitions and other embodiments are possible aswell. FIG. 21 illustrates transition from the CHARGE (GPT BASE) state1014 to HOT TURNING (CPT SLOW ROLLING) state 1018, with intermediatetransitional states 1102, 1104 occurring sequentially in between. Eachof the subsystem states is described elsewhere herein.

E. Generation to Hot Turning (PHES System Shutdown)

This use case is illustrated in FIG. 10 as the transition fromGeneration mode 1004 to Hot Turning mode 1006, and in FIG. 11 as thetransition from operating state 1016 to operating state 1022.

FIG. 22 further illustrates this use case. FIG. 22 is a state diagramillustrating operating and transitional states in a PHES system,including PHES system 1000, according to an example embodiment. Theseare example state transitions and other embodiments are possible aswell. FIG. 22 illustrates transition from the GENERATION (CPT BASE)state 1016 to HOT TURNING (GPT SLOW ROLLING) state 1022, withintermediate transitional states 1108, 1110 occurring sequentially inbetween. Each of the subsystem states is described elsewhere herein.

F. Hot Standby to Cold Dry Standby (PHES System Shutdown)

This use case is illustrated in FIG. 10 as the transition from HotStandby mode 1008 to Cold Dry Standby mode 1010 to, and in FIG. 11 asthe transition from operating state 1024 to operating state 1030.

G. Charge to Generation (PHES System Mode Switch)

This use case is illustrated in FIG. 10 as the transition from Chargemode 1002 to Hot Turning mode 1006 to Generation mode 1004, and in FIG.11 as the transition from operating state 1014 to operating state 1018to operating state 1028.

FIG. 23 further illustrates this use case. FIG. 23 is a state diagramillustrating operating and transitional states in a PHES system,including PHES system 1000, according to an example embodiment. Theseare example state transitions and other embodiments are possible aswell. FIG. 23 illustrates transition from the CHARGE (GPT BASE) state1014 to HOT TURNING (CPT SLOW ROLLING) state 1018, with intermediatetransitional states 1102, 1104 occurring sequentially in between. FIG.23 further continues with illustration of the continuing transition fromHOT TURNING (CPT SLOW ROLLING) state 1018 to GENERATION (CPT SLOW ROLL)state 1028, with intermediate transitional states 1116, 1118 occurringsequentially in between. Each of the subsystem states is describedelsewhere herein.

The invention claimed is:
 1. A pumped heat energy storage system, thesystem comprising: a charge compressor system; a charge turbine system;a generation compressor system; a generation turbine system; a hot-sideheat exchanger (“HHX”) system; a recuperator heat exchanger (“RHX”)system; a cold-side heat exchanger (“CHX”) system; a hot-side thermalstorage (“HTS”) system; a cold-side thermal storage (“CTS”) system; aworking fluid loop comprising: a first working fluid path arranged tocirculate a working fluid through, in sequence, the charge compressorsystem, the HHX system, the RHX system, the charge turbine system, theCHX system, the RHX system, and back to the charge compressor system, asecond working fluid path arranged to circulate the working fluidthrough, in sequence, the generation compressor system, the RHX system,the HHX system, the generation turbine system, the RHX system, the CHXsystem, and back to the generation compressor system, and a thirdworking fluid path arranged to recirculate at least a portion of theworking fluid through the charge turbine system without circulating atleast the portion of the working fluid through the CHX system, the RHXsystem, the charge compressor system, and the HHX system.
 2. The systemof claim 1, further comprising: an inventory control system, wherein theinventory control system includes a valve system operable to direct theworking fluid from at least one of the first working fluid path or thesecond working fluid path into at least one tank system, wherein thevalve system is further operable to add the working fluid from the atleast one tank system to at least one of the first working fluid path orthe second working fluid path.
 3. The system of claim 1, furthercomprising: another working fluid path arranged to recirculate at leasta portion of the working fluid through the charge compressor systemwithout circulating at least the portion of the working fluid throughthe HHX system, the RHX system, the charge turbine system, and the CHXsystem.
 4. The system of claim 3 further comprising a heat exchanger inthe other working fluid path.
 5. The system of claim 1, furthercomprising: another working fluid path arranged to recirculate at leasta portion of the working fluid through the generation compressor systemwithout circulating at least the portion of the working fluid throughthe RHX system, the HHX system, the generation turbine system, and theCHX system.
 6. The system of claim 1, further comprising: anotherworking fluid path arranged to recirculate at least a portion of theworking fluid through the generation turbine system without circulatingat least the portion of the working fluid through the RHX system, theCHX system, the generation compressor system, and the HHX system.
 7. Thesystem of claim 6 further comprising a heat exchanger in the otherworking fluid path.
 8. The system of claim 6 further comprising a fan inthe other working fluid path.
 9. The system of claim 1, furthercomprising: a bypass working fluid path arranged to circulate at least aportion of the working fluid from an outlet of the generation compressorsystem to an inlet of the generation turbine system without circulatingat least the portion of the working fluid through the RHX system and theHHX system.
 10. The system of claim 1, further comprising: a bypassworking fluid path arranged to circulate at least a portion of theworking fluid from an outlet of the generation turbine system to aninlet of the CHX system without circulating at least the portion of theworking fluid through the RHX system.
 11. The system of claim 1, furthercomprising: a bypass working fluid path arranged to circulate at least aportion of the working fluid from an outlet of the generation compressorsystem to a low-pressure side of the RHX system without circulating atleast the portion of the working fluid through a high-pressure side ofthe RHX system, the HHX system, and the generation turbine system. 12.The system of claim 1, further comprising: a first charge isolationvalve in the first working fluid path between an outlet of the chargecompressor system and an inlet of the HHX system; and a second chargeisolation valve in the first working fluid path between an outlet of theRHX system and an inlet of the charge turbine system.
 13. The system ofclaim 1, further comprising: a first generation isolation valve in thesecond working fluid path between an outlet of the generation compressorsystem and an inlet of the RHX system; and a second generation isolationvalve in the second working fluid path between an outlet of the HHXsystem and an inlet of the generation turbine system.
 14. The system ofclaim 1, further comprising an ambient heat exchanger (“AHX”) systemarranged in the second working fluid path between an outlet of alow-pressure side of the RHX system and an inlet of the CHX system. 15.A method of operating a pumped heat energy storage system, the methodcomprising: opening a first charge isolation valve in a first workingfluid path between an outlet of a charge compressor system and an inletof a hot-side heat exchanger (“HHX”) system; opening a second chargeisolation valve in the first working fluid path between an outlet of arecuperator heat exchanger (“RHX”) system and an inlet of a chargeturbine system; closing a first generation isolation valve in a secondworking fluid path between an outlet of a generation compressor systemand an inlet of the RHX system; closing a second generation isolationvalve in the second working fluid path between an outlet of the HHXsystem and an inlet of a generation turbine system; circulating aworking fluid in the first working fluid path through, in sequence, thecharge compressor system, the HHX system, the RHX system, the chargeturbine system, a cold-side heat exchanger (“CHX”) system, the RHXsystem, and back to the charge compressor system; opening a valve thatpermits recirculation of a quantity of the working fluid through thegeneration turbine system without circulating the quantity of theworking fluid through the RHX system, the CHX system, the generationcompressor system, and the HHX system; and recirculating the quantity ofthe working fluid through the generation turbine system withoutcirculating the quantity of the working fluid through the RHX system,the CHX system, the generation compressor system, and the HHX system.16. The method of claim 15, further comprising: opening a firstinventory control valve that releases at least a portion of the workingfluid from the first working fluid path into at least one tank system;and closing the first inventory control valve, thus storing at least theportion of the working fluid in the at least one tank system.
 17. Themethod of claim 15, further comprising: opening a first inventorycontrol valve that adds an amount of the working fluid from at least onetank system to the first working fluid path; and closing the firstinventory control valve.
 18. The method of claim 15, further comprising:opening a valve that allows at least a portion of the working fluid torecirculate through the charge compressor system without circulating atleast the portion of the working fluid through the HHX system, the RHXsystem, the charge turbine system, and the CHX system; and recirculatingthe at least the portion of the working fluid through the chargecompressor system without circulating at least the portion of theworking fluid through the HHX system, the RHX system, the charge turbinesystem, and the CHX system.
 19. The method of claim 15, furthercomprising: opening a valve that permits recirculation of a quantity ofthe working fluid through the generation compressor system withoutcirculating the quantity of the working fluid through the RHX system,the HHX system, the generation turbine system, and the CHX system; andrecirculating the quantity of the working fluid through the generationcompressor system without circulating the quantity of the working fluidthrough the RHX system, the HHX system, the generation turbine system,and the CHX system.
 20. A method of operating a pumped heat energystorage system, the method comprising: closing a first charge isolationvalve in a first working fluid path between an outlet of a chargecompressor system and an inlet of a hot-side heat exchanger (“HHX”)system; closing a second charge isolation valve in the first workingfluid path between an outlet of a recuperator heat exchanger (“RHX”)system and an inlet of a charge turbine system; opening a firstgeneration isolation valve in a second working fluid path between anoutlet of a generation compressor system and an inlet of the RHX system;opening a second generation isolation valve in the second working fluidpath between an outlet of the HHX system and an inlet of a generationturbine system; and circulating a working fluid in the second workingfluid path through, in sequence, the generation compressor system, theRHX system, the HHX system, the generation turbine system, the RHXsystem, a cold-side heat exchanger (“CHX”) system, and back to thegeneration compressor system; and opening a valve that permitsrecirculation of a quantity of the working fluid through the chargeturbine system without circulating the quantity of the working fluidthrough the CHX system, the RHX system, the charge compressor system,and the HHX system; and recirculating the quantity of the working fluidthrough the charge turbine system without circulating the quantity ofthe working fluid through the CHX system, the RHX system, the chargecompressor system, and the HHX system.
 21. The method of claim 20,further comprising: opening a first inventory control valve thatreleases working fluid from the first working fluid path into at leastone tank system; and closing the first inventory control valve, thusstoring working fluid in the at least one tank system.
 22. The method ofclaim 20, further comprising: opening a first inventory control valvethat adds working fluid from at least one tank system to the firstworking fluid path; and closing the first inventory control valve. 23.The method of claim 20, further comprising: opening a valve that permitsrecirculation of a quantity of the working fluid through the chargecompressor system without circulating the quantity of the working fluidthrough the HHX system, the RHX system, the charge turbine system, andthe CHX system; and recirculating the quantity of the working fluidthrough the charge compressor system without circulating the quantity ofthe working fluid through the HHX system, the RHX system, the chargeturbine system, and the CHX system.
 24. The method of claim 20, furthercomprising: opening a bypass valve that permits circulation of aquantity of the working fluid from the outlet of the generationcompressor system to the inlet of the generation turbine system withoutcirculating the quantity of the working fluid through the RHX system andthe HHX system; circulating the quantity of the working fluid from theoutlet of the generation compressor system to the inlet of thegeneration turbine system without circulating the quantity of theworking fluid through the RHX system and the HHX system; closing thefirst generation isolation valve; and closing the second generationisolation valve.
 25. The method of claim 20, further comprising: openinga bypass valve that permits circulation of at least a portion of theworking fluid from an outlet of the generation turbine system to aninlet of the CHX system without circulating at least the portion of theworking fluid through the RHX system; and circulating at least a portionof the working fluid from the outlet of the generation turbine system tothe inlet of the CHX system without circulating at least the portion ofthe working fluid through the RHX system.
 26. The method of claim 20,further comprising: opening a valve that permits circulation of at leasta portion of the working fluid from the outlet of the generationcompressor system to a low-pressure side of the RHX system withoutcirculating at least the portion of the working fluid through ahigh-pressure side of the RHX system, the HHX system, and the generationturbine system; and circulating at least the portion of the workingfluid from the outlet of the generation compressor system to thelow-pressure side of the RHX system without circulating at least theportion of the working fluid through the high-pressure side of the RHXsystem, the HHX system, and the generation turbine system.
 27. A pumpedheat energy storage system, the system comprising: a charge compressorsystem; a charge turbine system; a generation compressor system; ageneration turbine system; a hot-side heat exchanger (“HHX”) system; arecuperator heat exchanger (“RHX”) system; a cold-side heat exchanger(“CHX”) system; a hot-side thermal storage (“HTS”) system; a cold-sidethermal storage (“CTS”) system; a working fluid loop comprising: a firstworking fluid path arranged to circulate a working fluid through, insequence, the charge compressor system, the HHX system, the RHX system,the charge turbine system, the CHX system, the RHX system, and back tothe charge compressor system, a second working fluid path arranged tocirculate the working fluid through, in sequence, the generationcompressor system, the RHX system, the HHX system, the generationturbine system, the RHX system, the CHX system, and back to thegeneration compressor system, and a third working fluid path arranged torecirculate at least a portion of the working fluid through thegeneration turbine system without circulating at least the portion ofthe working fluid through the RHX system, the CHX system, the generationcompressor system, and the HHX system.
 28. The system of claim 27,further comprising: an inventory control system, wherein the inventorycontrol system includes a valve system operable to direct the workingfluid from at least one of the first working fluid path or the secondworking fluid path into at least one tank system, wherein the valvesystem is further operable to add the working fluid from the at leastone tank system to at least one of the first working fluid path or thesecond working fluid path.
 29. The system of claim 27, furthercomprising: another working fluid path arranged to recirculate at leasta portion of the working fluid through the charge compressor systemwithout circulating at least the portion of the working fluid throughthe HHX system, the RHX system, the charge turbine system, and the CHXsystem.
 30. The system of claim 29, further comprising a heat exchangerin the other working fluid path.
 31. The system of claim 27, furthercomprising: another working fluid path arranged to recirculate at leasta portion of the working fluid through the generation compressor systemwithout circulating at least the portion of the working fluid throughthe RHX system, the HHX system, the generation turbine system, and theCHX system.
 32. The system of claim 27, further comprising a heatexchanger in the third working fluid path.
 33. The system of claim 27,further comprising a fan in the third working fluid path.
 34. The systemof claim 27, further comprising: a bypass working fluid path arranged tocirculate at least a portion of the working fluid from an outlet of thegeneration compressor system to an inlet of the generation turbinesystem without circulating at least the portion of the working fluidthrough the RHX system and the HHX system.
 35. The system of claim 27,further comprising: a bypass working fluid path arranged to circulate atleast a portion of the working fluid from an outlet of the generationturbine system to an inlet of the CHX system without circulating atleast the portion of the working fluid through the RHX system.
 36. Thesystem of claim 27, further comprising: a bypass working fluid patharranged to circulate at least a portion of the working fluid from anoutlet of the generation compressor system to a low-pressure side of theRHX system without circulating at least the portion of the working fluidthrough a high-pressure side of the RHX system, the HHX system, and thegeneration turbine system.
 37. The system of claim 27, furthercomprising: a first charge isolation valve in the first working fluidpath between an outlet of the charge compressor system and an inlet ofthe HHX system; and a second charge isolation valve in the first workingfluid path between an outlet of the RHX system and an inlet of thecharge turbine system.
 38. The system of claim 27, further comprising: afirst generation isolation valve in the second working fluid pathbetween an outlet of the generation compressor system and an inlet ofthe RHX system; and a second generation isolation valve in the secondworking fluid path between an outlet of the HHX system and an inlet ofthe generation turbine system.
 39. The system of claim 27, furthercomprising an ambient heat exchanger (“AHX”) system arranged in thesecond working fluid path between an outlet of a low-pressure side ofthe RHX system and an inlet of the CHX system.